Alright. Since you apparently don't know what those mean, I'll explain 'em to you. (b'')b
A sweeper is a pokemon made to attack. Be it with physical attacks, special attacks, or both, that is its purpose. They are commonly used as leads, and most teams have at least three. You do, always, need at least two. A team with no offence is a team that crashes, burns, and dies a horrible death to one that possesses any modicum of basic skill.
A wall is a Pokemon designed to sop up damage. An effective wall will leave your opponent with no choice but to switch out. They can be used to block physical attacks, special attacks, or both. Walls have high def and/or sp def, and high hp. Blissey is a brilliant example of a sp wall, with the highest hp in the game and terrific sp def to boot.
A revenge killer is used to kill a Pokemon that has just killed you by using arena trap or mean look, outspeeding it, or using pursuit as it switches. It takes out threats that you're having difficulties with. Dugtrio, with its high spd, att, and its arena trap ability is a good example.
A staller is used to buy turns that you can use to heal your Pokemon, get rid of weather/stealth rock/spikes, or just getting rid of the PP of one of your foe's particularly nasty moves. Shuckle is, in my opinion, the best staller.
There are some other types, but I'll get to them later, maybe.
