You can use skills as soon as you can add points to them (there is probably an 'apply' button you need to hit after you distribute the points with the arrow buttons). Merchants can sell equipment with skill bonuses, but that is it for their involvement in the skill system.
In the Xbox version you can assign skills to the face buttons or d-pad directions, or pause the game and hit a shoulder button to bring up a menu where you can use items, potions or skills that do not need a target (like Healing or Summon Ghost).
To assign skill to hotkeys in the PC version, from a couple different topics:
How are you assigning skills to quickslots? There are a couple of ways:
1) Keep the numerical key on your keyboard pressed for +- 2 seconds.
2) In pause mode, right click on the slot you want to quickmap.
3) In the skill screen, drag the skill icon to the quickslot.
Which of these options are you using and can you try the others?
It'd help which skill you were trying to hotkey because, not all skills are hotkeyable. For the ones that are, you Left-Drag the skill into one of the slots and click when the slot lights up. From my experience, those slots don't become active (light up) unless you aim towards the very bottom of the slots. I think they did that so that you couldn't accidentally move something out of the bar. They must never have heard of "Locking" the action bar.
Lovis' tower is number 2 on that screenshot (north of the central lake). You will need to complete enough of the starting section to get access to the full Broken Valley, after which the tower should be easy to find. Even then, though, the opponents around there may be a little tough, and there are some off to the southeast and west (then up a mountain trail) you may want to do first. About level 9, or so, you shouldn't have much trouble, though there is no rush to make it there (despite a certain NPC's suggestions later).
