In the first part, a goalie, two central defenders play against a striker (3vs1)
The central defenders try to play the deepest man (striker)
The striker is positioned deep and is defended by two central defenders (build up the degree of defence)
When the striker is reached, the two outfield players are allowed to join in and these players will join in under the striker, creating a 3vs2 situation (5vs3 in total)
After a shot from the attacking side, the trainer will play a 2nd ball to the striker or outfield players of the other side.
This also creates a 3vs2 situation there (5vs3 in total)
This way this form continues and the goalkeeper takes turns with the 'build-up'.