A very wide question.
In dinghy (small boat) sailing, the RYA method teaches 'five essentials'
Sail setting
Centreboard
Balance (side to side)
Trim (fore and aft balance)
Course sailed (which is about tacking, allowing for tides etc. Basically, it is about the direction the boat is moving rather than the direction it is pointing)
Note that the rudder is not one of the five essentials, it is possible to steer round a course without it.