Imbalances In chess
Some of the major imbalances between N and B are probably mobility and attacking/defense characteristics. N's aren't very mobile but can attack anywhere from usually many directions. They often also aren't the best for defense. B's can be more mobile but are more easily restricted by square color and blocking. But might be better defenders. Much has to do with how you can set up the board to fit your piece vs. your opponent.
Differences might become more noticeable in late middle game or endgame.
One way to get a feel for them is to take 2 pawns off each side, though not the same ones, with only a B for one player and a N for the other. Play a bunch of games and you'll probably be pretty knowledgeable about N vs. B after a little while.