One reason that the bishop is worth slightly more than the knight is that the bishop can dominate the knight in an open board. In the following diagram, you can see that the white Bishop controls every square that the black knight can reach.
To improve, players should gain experience in several ways. These lessons are fine, but you should play against others and review the games of the great players. As you play through master games, again and again, you will see bishops three squares away from enemy knights, dominating them as in the diagram above.