Some skills are passive and some are more like spells, they have to be selected and then cast on the target. The passive ones have their icons greyed out and are always running in the background, bestowing whatever particular benefit upon you at all times.
Repair may not seem to work sometimes because if your repair skill is only at level one, it only repairs 20% (I think) of an item's durability, so if you have something that is at 5/10, attempting to repair it further with a skill level 1 won't show any result. If the item was at 1/10, however, you'd see it repaired to 2. (If my 20% is the correct number.)
I'm sure there will be a flurry of more complete responses by the time I hit the complete key....
