There's quite a bit more detail to it than that, unfortunately. An amount of detail that no new player should be expected to know before they can play the game, and yet here we are. Amidst a community that constantly tries to get each other banned and a ruleset enforced by GMs that, in my honest opinion, does far more harm than it does good.
That being said, I'm going to give you a bit of an explanation to help you understand how you should roll on items. Hopefully it'll help you to progress your character and avoid getting a ban.
#1
If you're not sure, ask the group. If they don't respond or give you a for sure answer, use the GREED roll.
#2
You are expected to use certain kinds of stats. This is going to be a long one, so buckle up.
- The "Stamina" stat is generally seen as a "Tank" stat, even though everyone can and should use it. But if an item has only stamina on it, and the tank wants the item, you will be expected to let the tank have it.
- "Defense", "Armor", "Dodge", "Parry", "Block" are all also tank stats. Avoid rolling need on these items if you are not a tank, unless you get explicit consent from the tank and the group to roll on the item.
- "Spirit" and "Mp5" are the same as the above mentioned stats, except they are healer stats. Can be loosely used by caster dps.
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- "Agility" is typically reserved for Feral Druids, Rogues, Enhancement (melee) Shaman, and Hunters. It is also useful for Warriors, Paladins and Death Knights, but it is more of a secondary stat for them.
- "Strength" is the same as Agility, but instead it is used for Warriors, Paladins (tank and dps only), and Death Knights. It is also useful for Feral Druids, Rogues and Enhancement (melee) Shamans to some degree, but it is secondary for them.
- "Intellect" is the same as both Agility and Strength, but it is for casters. Casters include dps casters and healers. These include Warlocks, Priest, Mages, Shaman (Elemental and the healer spec, Restoration), healer Paladins, and Druids (Balance and the healer spec, Restoration). The stat also benefits Paladin tanks and dps, Enhancement (melee) Shaman, and Hunters to a lesser extent.
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- "Armor Penetration" is exclusively for melee dps and Hunters. People will complain about dps Paladins using it, but it's still useful for them to some degree.
- "Attack Power" is for melee dps (Retribution Paladin, Warrior, Death Knight, Rogue, Feral Druid, Enhancement Shaman) and Hunters. It serves a very similar purpose as Agility and Strength do.
- "Spell Power" is for caster dps and healers. The stat is used by pretty much the same list of classes that use Intellect.
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All that said about stats, if I did not list the stat being a main stat for a certain class, then people are going to expect you to greed on the item. If the stat is secondary for you, and you need roll on it, you will probably get called a ninja.
#3
Always, always, ALWAYS try to keep only to using the highest available armor class available to your character class. This refers to the 4 types of armor classifications, which are Cloth, Leather, Mail and Plate. This rule will only apply to when you're playing with random people. You will find that it does not always apply when playing with competent players or in a guild, because for example, some leather items are good for a Warrior, even though they can wear plate armor.
The character classes fall into armor classes as follows;
Cloth - Warlock, Priest, Mage
Leather - Druid, Rogue
Mail - Hunter, Shaman
Plate - Paladin, Warrior, Death Knight
-------------- Paladins and Warriors can only use Mail armor until level 40.
Caveats for max level;
> Cloth armor has the possibility of being good for Balance and Restoration Druids, Elemental and Restoration Shamans and Holy Paladins.
> Leather armor has the possibility of being good for (Intellect leather) Elemental and Restoration Shamans and Holy Paladins, OR (Agility leather) Hunters, Enhancement Shamans, Paladins, Warriors and Death Knights.
> Mail armor has the possibility of being good (Intellect mail) Holy Paladins, OR (Agility mail) Retribution Paladins and very limited use for Warriors and Death Knights.
#4
ONLY if the item fits the above criteria PERFECTLY for you, will you be allowed to roll NEED.
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That all being said, realistically, you should investigate the stats that your class and specialization use, and try to aim for those. Unfortunately, sometimes the stats you want will be on items that the community thinks you shouldn't have (usually happens when armor class is the issue), which will put kinks in your leveling and gearing process when playing the game with people you don't know.
I would strongly advise you finding a decent guild to play with. This is usually the best and most resolute solution to this problem.