I would provide pics but the servers are down for maintenance, so I'll do my best through words. Every action has a cost to be added to the action bar. As long as you have enough action points, you can add abilities. Once you are in the actions menu all you have to do is click on the box (slot) you want that action to fill. On the right side, near the top, there is a small arrow. If you click this arrow a dropdown list appears that gives you the different classes which you have actions available. All you have to do is click the class you want and available actions should load into the box. Now just click the action you want and a small dialog box will pop up asking if you would like to add it to the main hand or off hand. I'm not entirely sure how this works, but you'll most likely be picking main hand. Upon doing, the chat window should say "(Name of action) added to slot #" and the actions icon will populate that spot.