No, I think you got it all wrong. There are two types of skills:
Passive skills: These skills are used automatically throughout the game. Like increased sword damage is automatic. You don't have to activate the skill, the game will calculate the extra damage during your hits.
Active skills: These skills you have to use yourself when you want to use them. Like a fireball.
To select a skill you already invested skillpoints in, press the second little hand next to your characters picture. You will then see all of your active skills. You can choose one.
To use an active skill during the game, use the right mouse button.
Tovi 