When charging, the first model you move must end within 1/2" of an enemy model. You can do this any way you want; any model from the charging unit can be moved first, any distance (up to the result of the charge roll), in any direction, so long as it ends within 1/2" of an enemy model. You do not need to move towards the closest enemy, nor move the model that is closest first (you also do not need to declare a target for the charge in the first place).
After that, each other model moves a distance up to the result of the charge roll. Like any other move, they must end this in coherency.
This means that with a sufficient charge roll you can hop straight over an enemy unit and land behind it, which is a pretty common tactic for flying units.
Does that make sense?