Sweppers,tank, ect.(Credit to MG for making this guide)

Lead -
This is the one you start off with, and perhaps not the one
you'll end with. Leads are meant to set-up Stealth Rocks for more damage
over time, or screw with the other Lead (Anti-Leads). After they've
fulfilled their purpose, they're pretty much yesterday's garbage and
have nothing left to do but either cause as much damage as it possibly
can, or be used as death fodder. Some common leads are Azelf, Abomasnow,
Weavile, Infernape, and Mamoswine. Sometimes leads will have explosion
to get rid of one of the opponents pokemon.

Sweeper
These
Pokemon are usually fast and have high ratings in Attack or Special
Attack. Their job is simply to strike hard and deal as much damage as
possible. It's pretty self-explanatory. Many examples of sweepers are
Electivire, Breloom, Alakazam, Flygon, etc. There are also mixed
sweepers that have an EV spread set up to use both Special Attack and
Attack effectively, these are the sweepers that have a better chance
against walls. Some sweepers carry Choice items for that extra kick.

Wall -
Trading
offense for superior defenses, these Pokemon are meant to take hits
like a brick wall. They give sweepers a hard time and most have
Leftovers or recovery moves that help them stay in longer. When looking
for good walls, take typing into consideration. Since walls don't often
have decent attack ratings, it'd be smart to give them moves that
cripple the other player's team, such as Stealth Rocks, Thunder Wave,
Will-O-Wisp, etc.

Tank -
The bastard child of a wall and
sweeper. Tanks have decent defenses and in return can dish out
impressive damage. Tanks are for those that can be indecisive when
deciding whether to use a certain sweeper or wall in a team. After all,
it may save you an extra spot on your team. Good examples of tanks are
Snorlax, Steelix, Metagross, Hippowdon, the list goes on. .

Set-Up Sweeper -
Pokemon
that use boosting moves such as Dragon Dance, Swords Dance, Calm Mind,
Nasty Plot, and the like are what I consider a Set-Up Sweeper. Some of
them start off frail or weak, but can end up even tougher than walls or
stronger than your standard sweepers. It's always nice to have one up
your sleeve, the key is choosing the right moment. Examples of Set-Up
Sweepers can be Mismagius (Calm Mind), Scizor (Swords Dance), Dragonite
(With Dragon Dance), Togekiss (Nasty Plot),

Baton Passer -
These
Pokemon have the move Baton pass and are normally used to pass on
boosts from stat raising moves and Substitutes. They're a great addition
to team members that don't have stat raising moves of their own.
Imagine using Curse six times with Umbreon and passing that to Dusknoir.
Two words: Super Tank. There are also some pretty creative ways to use
Baton Pass; some of them being by manipulating Substitute to activate a
berry, or keeping effects like Yawn and Mean Look intact. Any Pokemon
that has this move pretty much falls into this category.

Sabotage -
A
good analogy to compare this to would be that one bully on the beach
that kicks in sand castles. The main purpose of these Pokemon are to
(pardon my language) entirely deuce up the other player's team. They can
carry moves like Roar, Whirlwind, or Haze to ruin Set-Up sweepers, or
Taunt to stop non-damaging moves altogether. On the offensive side, they
can have Spikes, Toxic Spikes, and Stealth Rocks to shorten the
lifespans of anything the other player has to send in, normally Stealth
Rocks is all you need to ruin frail types with Focus Sash. Other
sabotage moves are Rapid Spin, to stop the enemy Stealth Rocks, Toxic,
to limit the survivability of walls and tanks, Will-O-Wisp to burn and
cut the attack of physical attackers, Thunder Wave, to slow down the
other Pokemon and maybe cause some major paralysis annoyance, or even
Trick to give the opponent an unwanted item. Some even set up
Reflect/Light Screen to cut the offensive prowess of the opposing team.
Trick Room can mess with many sweepers. A lot of the time, walls are
used to carry sabotage moves.

Clerics -
Pretty
self-explanatory, these Pokemon carry moves that either heal or cure
status conditions of its fellow team members. They usually have good
defenses, and carry moves like Wish, Aromatherapy, and Heal Bell to
increase the survivability of your team. They often have healing moves
for themselves to help them last longer. Clerics are really helpful
especially when a battle drags on too long.