First you need to find a camping site. Around these camping sites are usually 3 elemental outlets. If you walk up to them you can absorb their power.
Once you have absorbed one, we will use fire for this example, go into your menu and select Elemancy. Once in this selection you can select and empty location on the right. This will move your cursor to the elemental left side of the window. Here you can mix and match different amounts of elements in order to create the spells that you want to cast. Just select the element you want and press RB once to put some elemental power into the spell. If you chose fire then you will have a window on the bottom left that says Fire X 3 with a 1 under potency. If you want the spells to hit harder then max out the potency. You only need the 1 point for the achievement though.