In chess there are 3 phases to a match, the opening, the middlegame and the endgame. When you talk about opposition in terms of chess it takes place in the endgame when there are the kings and a few pawns. The opposition is when the king blocks the other king because they can never touch. In the example below you can see what it looks like.
This is what the opposition looks like. What it is at it's simplest definition is a king blocking a king so the king is forced to retreat/not move forward. A tip on when to use it is when the enemy king sees your pawn(when the king is in your pawn's path)
Distant Opposition
The distant opposition is when you are parallel to the enemy king so that if they move the king forward you mirror them and in a sense, winning a tempo. It can be seen in the example below.
As you can see black had the distant opposition which allowed him to gain the regular opposition.
Puzzles
Gain The Opposition as Black
Use The Opposition To Win