The batter is together with the bowler the player that runs the game. The task of the batsman, another name for batter, is to defend the wicket and to score runs.
There are two batsmen on the field, one is the striker and stands on the wicket opposite to the bowler. The other batsman, also called non-striker, is opposite to the striker therefore on the wicket of the bowler.
The striker and the non-striker swap roles every over, or if the batsman scored 1, 3 or 5 runs; because then the non-striker is opposite to the bowler.
The striker will have to decide first if he wants to bat leg-stump (on-stump), middle-stump or off-stump. He then puts his bat vertical parallel to the stump on the ground and moves it in a virtual line to the batting crease. When he has done that, he will ask an umpire to check if he is on the same heights as the stump he plans to bat on. The umpire will go behind the opposite wicket and tell him if he has to move the bat or is at the right position. Then the batsman will mark this position with his shoe or bat, so he will remember were it is.
Now the game can start. Normally, the batsman will stand with one foot behind the batting crease and one over the batting crease. If he is right handed, he will have his right foot behind the batting crease, if left handed, the other way round.
He leaves his one foot behind the batting crease, because then he can not be stumped out. Remember, a batsman can only get stumped if no part of his body or bat is behind the batting crease.
A lot of batsman move their bat up and down, hitting the pitch or their shoe. They do that to stay concentrated and to react faster when the ball comes. Also a lot of batsmen do a small step with their right foot to their right (if they are right handed, if they are left handed off course in the other way round), in the direction of the wicket and to the front. They do that to have more room to move, because when they stand ready to bat, they have their feet quite close together.
When the ball comes, they position themselves in order to hit it right, where they want to hit it. Remember, they can hit it everywhere they want, in every direction they want.