Hey! I see you have trouble understanding what a sweeper/wall/tank is. So here are some definitions:
Sweeper-A pokemon with high speed and an offensive stat that is used mainly for attacking and fainting other pokemon, they typically have low defenses. A pokemon can be a physical or a special sweeper based off their offensive stats. If both are high, they are considered a mixed sweeper. For example, Gengar, Salamence, etc.
Wall-A wall usually has high defenses, low speed, and low offensive stats. These pokemon are used to inflict status effects on the opponent, as well as absorb attacks that their sweeping teammates cannot. Toxic/protect is a very common move combo to use with a wall. They usually have types that have lots of resistances or very few weaknesses, like Steel. For example, Skarmory, Blissey, Ferrothorn, Jellicent.
Tank-Not to be mistaken for a wall, a Tank is a pokemon with high offensive and defensive stats. They hit hard with attacks, while absorbing them at the same time. They are pretty versatile and can fit several situations. For example Conkeldurr, Magnezone..