Status problems are very important to Pokémon battling. You can only have one status condition at a time, but confusion affects a Pokémon at the same time as another status problem. Here are the status problems you’ll encounter, and what they do.
Poison hurts your Pokémon during battle by 1/8 (1/16 in Red, Blue, and Yellow) of its HP each turn. Being badly poisoned means the poison will get worse every turn, but it instead starts at 1/6 HP on the first turn, and increase to 2/16 HP on the second, and so on. Poison also lingers after battle. In every game before Black and White, Poison hurts the Pokémon by 1 HP every 4 steps outside of battle as well. In Diamond, Pearl, Platinum, HeartGold, and SoulSilver, it wears off outside of battle when it has only 1 HP remaining, however. Poison-type Pokémon cannot be poisoned.
When you Pokémon is Paralyzed, its speed gets lowered to 25% of its maximum speed, and cannot move on its turn 25% of the time.
Burn lowers your Pokémon’s attack by 50% of its maximum attack. It also hurts your Pokémon during battle by 1/8 (1/16 in Red, Blue, and Yellow) of its HP each turn, but not outside of battle like poison.
While your Pokémon is asleep, it cannot attack. Sleep lasts from 1-5 turns. In Red, Blue, and Yellow, Pokémon were not able to attack on the turn they woke up, but in every game after those, they are able to.
When your Pokémon is frozen it cannot move to attack. In every game after Red, Blue, and Yellow, Pokémon have a 20% chance of thawing out on each turn. Ice-type Pokémon cannot be frozen.
When a Pokémon is confused, it attacks itself in a battle 50% of the time as if a 40-power typeless physical attack hit it. Confusion wears off after a battle ends or the Pokémon is switched.