The whole bishop v night thing

Which oen to use first and witch are better?

At your level it does not even matter, keep focusing on improving you chess, when you get to 2400 rating then start thinking about that question.

@tiridates I want to know which one to use first.

Knights before bishops, because they are not easily targeted and control more central squares.
Which ones are better? Bishops in open positions, knights in closed.

But these are just general principles. What you move and when you move it or what you keep or exchange depends obviously on the position on the board.

@bufferunderrun Then how should I choose between knight and bishop and or what square to do them onto

Depends on what you are trying to achieve and what position on the board demands.
There are ideas behind the moves. Take Ruy Lopez for example, 3. Bb5. Why? It undermines control over e5 and discourages d5.

Your question is as complicated as chess I guess. You're looking for the best places on the board for all of your pieces. Knights and bishops are likely to do better when posted in places where they cannot be attacked, especially attacked by pawns. Usually knights are well posted on the F or C file as a start, they both attack into the middle and defend from there. They can be really great if they can be safely moved to the 4th, 5th, or maybe 6th rank in a fairly central place.

Bishops can do best on long open diagonals especially where they are bearing down on the enemy king and his nearby defenders.

I guess the question you should always be asking is what can I do to get this piece into the game, that is into the action.

@bufferunderrun then how do I deduce the ideas and make skill moves?

@JunoCunerino What is a long diagonal in chess?

By studying openings, middle games, endgames, games of strong players and analyzing your own games.