To answer the other part of your question.
When you buy skill level X, that means that you can now use your skill points to train it up to level X. You don't actually GET any skill for your purchase - you get the ability to train.
So if you buy the hammer skill in the battleground at the start of act two that means you can train it up to level 2. If you try and raise it higher nothing happens. Now suppose you visit the hermit and buy hammer 5. You still have the skill at level 2. But if you have some skill points lying around (or unlearn some other skill to free them up) you can click on that little + and now the number will go higher than two - all the way to five. Later you can raise it even more.
Clear now?
