Knowing how much your pieces are worth is important.  This chart gives you a good idea.   You can’t put a value on the king as losing it ends the game.

So a bishop and a knight (3+3=6) are worth roughly a rook and a pawn (5+1=6).

And a queen is worth roughly a rook, bishop and pawn (5+3+1=9).

But remember, everything depends on the position, so keep thinking!