You have three kinds of abilities: Actions, Morale and Tactics. Actions are your "go-to" abilities; the ones you will use most often. Morale skills are your super duper charge-up abilities; these can make or break a fight. Tactics are beneficial effects that are always on and can affect almost anything you might do.
Action abilities include a wide range of attacks, heals, buffs, debuffs, etc. and are used from your QuickBar.
Morale abilities are powerful "charge up" abilities. Morale is gained by being in combat, and once you have gained enough Morale to use your ability, you can click its icon to activate it. However, once you've used a Morale ability, you'll need to build more morale in order to use another one.
Tactics are enhancements that help you fight the way YOU want to. Are you going to charge headfirst into battle, or sneak around and stab your enemies in the back?
The number of available slots for tactics will increase as you level up.
To train new abilities, you'll need to visit your trainer. As you level up, you'll need to go to higher Warcamps to be able to train new abilities.
To change active Morale abilities, Action abilities and Tactics, click the "Abilities" button on the top left side of the UI. The window that pops up has a tab for "Actions", "Morale" and "Tactics". Click on the pertinent tab, and then click on the ability you wish to add, and finally click on the slot you wish to add the ability.