You must "equip" your skills first.
When you are outside, click on your profile, then on each skill/spell you want to use.
If you are fighting, click the question mark '?' instead.
Maybe we need a QTDDTOT.
Tbh I also expected that new skills/spells were automatically ready to use.
Furthermore, the question mark is unclear to me: maybe the gear symbol (for "settings") would fit better, I don't know.
Finally I find weird that I can't either cast spells on myself (e.h. heal or invigorate) or sort my skills (or those of my slaves) without going outside.