I'm writing this without looking at it right now since I don't have access so forgive me if it's not right.

I think you click on your trinity button on your minimap when you mouse over the four popup buttons they should say click for simple edit or right-click for a more complex set. One of them will bring up a box with three tabs at the bottom. Somewhere on the left tab is a button that says create. it will create a bar then you have to right click it and add buttons to it.

Hope that helps, could have been designed a little better I think, but I do like the new trinity bars.