When you attack an enemy base in Clash of Clans you need to think strategically in terms of positioning.
Positioning your troops can be the deciding factor of losing the attack to earning all three stars from the attack.
Once you deploy your troops they will attack completely on their own and cannot be directed in any way.
Each unit will attack depending on their own abiliites and their set targets. If you want to know what units attack what parts of the base check out our information for each unit on this website.
Hopefully this has answered your questions about directing your troops. Remember, place your troops where you want them to start attacking before you set out an all out attack on your enemy.