Rock Paper Scissor!
This is not necessarily a guide, but a discussion to explain to new players to RO in general the most basic mechanics of the game. This guide will not go into much detail on the "how to do" things, such as how to set your hot keys. If you are some-what new to the game, or even have been playing a long time and feel like having the right to say "i disagree!" please do read on.
I do disclaim that this guide is purely based on my personal experience only, and have not really studied the coding per se. Another major disclaimer is that I wrote this while bored at work in between cnn.com and actual work, so it may be bit wordy and/or disjunctive. Also, the below seems to be the basic ideas that most veterans are aware of that prepares and enables their mastery of the game. I am not trying to give you a guide like "Go buy Bathory Armor, and then this..." but rather telling you why you want to go buy bathory armor in principle, so that you can apply it generally.
What is this RPS?
First, Gravity copied this game from "Rock, Paper, Scissors." Basic mechanic is just that, rock beats scissors, paper beats rock, and scissors beats paper (RPS rule).
Every monster in the game, including your character, has a list of "Natures." The main and relevant ones are Race, Property, and Size. Every item in the game has characteristics as well, most important ones being Property, Slots, Breakability, Type, and Weight. (For TRO101, only property will be discussed, maybe items in general will be discussed in TRO103) I will leave level of monsters and level requirements of items out of this, as they are rather minor theoretically. Do note that both monsters/players and items have things called Stats, which work differently than Nature factors, and will discuss that later in maybe TRO102.
So moving along, as for monsters/players, Race, Property, and Size are 3 sets of a game of rock paper scissors. Size is very niche in terms of utilization so I will not discuss it. (Though making use of Size factors do create differences between those who do and don't, its one of the last things you want to consider). For Property, in RO there are Neutral, Fire, Water, Wind, Earth, Holy, Shadow, Undead, Poison, and Ghost. Now you have to think of each of those elements as a paper or rock. So for example, Water beats Fire which means Water does more damage to Fire. There are ties too, like Paper ties Paper. For example, Water ties Water, so instead Water does less dmg to water. So this is bit unique in that if Paper beats Rock, Rock loses to Paper, but differs a little bit in RO in terms of degree of winning/tying/losing due to the number of elements and use of percentages oppose to all or nothing. Why is this important? Because if monsters are Fire element, you want to use weapons or skills that are Water element to do more dmg. At the same time, keep in mind the degrees. Like, fire element monsters will take most dmg from water element, but will also take additional dmg from poison element as well. So ideal is Water, but Poison will do as well.
There are also element that become 100% ineffective when matched with the correct element. For example, if you are fighting a shadow monsters and use a shadow weapon, you will do no damage to them at all.
Although, if you use a poison weapon, you will do 50% dmg... while using a holy weapon will make you do 125% dmg. You can check out the actual Element Table right here(I assumed level 1 element for everything discussed here, and will not go into the level of elements here). Now you can gear yourself to do more dmg to monsters, but that's not all. The difference between a players element and a monster's element is that a player can change their natural element, which is neutral btw.
So the flip side is that, if a monster attacks you with a shadow element skill, you want to be a shadow element, which can be achieved by having a Bathory carded armor on. Every card that changes your natural element goes into the armor slot, so you will have to buy and switch between different carded armors. I just want to also note that for new players, there are indeed armor that is by nature is a certain element and has a slot for you to put in different cards than an element card. Also, note you can never be 2 different elements at the same time, so putting bathory in an armor with fire element nature will not work. (As to which takes precedent, i am not sure). So the RPS rule goes both ways, and players can utilize it to achieve awesomeness(?). However, this does not mean you need to buy every single elemental armor. Some are more useful than others and you should buy ones that match your habit or preference what and where you kill things. It is not necessarily because there are more monster of one kind than another, but rather because the return/reward of certain monsters in the game. For example, anubis is widely known to be one of the best leveling spots and Niff for zeny earning, and they are two of the reasons why Bathory Armor is one of the most in demand on the market. However, if you never plan to go to Anubis or Niff, and prefer Thor, you want to get a fire armor over bathory. Although, I will say bathory is a must in tRO if not all RO where it is obtainable as easily.
So the lesson is, know the monsters property and property of their skills (Important note: All monsters' normal attack is neutral damage, and hence why deviling garment is so important), and know your own property (neutral in absence of element armors) and the property of your attacks/skills. (It is important to know that all your own normal attacks always take on the element of your weapon, but only some skills taken on the element of your weapon. As to which is which, that's for you to ask around). So equipment wise, armors and weapons. There we go, now you know the basic principle as to how to do more damage and take less damage.
There is another factor that enables you to do more damage and take less damage. As I listed above, it is Race (Size being top tier niche, so not discussed). For Race, in Ro there are Demi-humans, Demons, Undeads, Insects, Plants, Angels, Formless, Brute, Fish, and Dragons. I will try to make this explanation bit shorter since now you have an understanding of RPS rule, hopefully. In fact, this one isn't fully RPS rule material as all you need to do is know the Race and counter it accordingly. However, a certain race's counter isnt necessarily another race, but just another card that impacts that Race. So for example, if you are fighting Anubis, which is Demi-human Race, you want to be wearing Toad or Cranial shields. Why? Because Toad and Thara Frog cards reduces damage from Demi-humans by a %. Race reduction cards always go into shield slot, so this is a shield card consideration for you which is also based on preference. Although again, there are monsters more useful to kill than others as mentioned above.
So that's how you take less damage. As for doing more damage, there are cards for weapon slots that will increase your dmg to certain classes. For example, Hydra cards will do more damage to Demi-Humans by a certain %. There are cards like Turtle General and Samurai cards that go into your weapon slot but affects your stats instead to do more damage, but that may be discussed in TRO102.
Pretty simple right? It is up to you to find out which are which though in all above cases, and such information is widely available if you look/ask around.
Do note that there are exceptions to everything, and especially to me saying Race dmg reduction card is only in shields, as there are probably certain items that have that effect in other slots. This is especially true with some custom and newer items on our server.
Hopefully now you have a better understanding now!
To understand it in a basic manner:
Different elements go into Armors.
Weapons have different elements.
Water > Fire.
Water element weapon/skill does more damage on Fire armors/monsters.
Fire element weapon/skill does less damage on Water armors/monsters.
Find out the monster's race.
Find the shield card that reduces dmg from that race.
Find the weapon card that increases dmg to that race.