When skills are unlocked and bound to your class, you can open your skills menu/gui and assign and upgrade your skills using skill points all in one place! When binding skills, you select slots 1-6 to bind them to that number. In order to cast, you can simply hit F while in survival mode in order to enter casting mode (visualized by custom particles), then hit any number you have bound to cast your skill. The action-bar pulls up a helpful list of your bound skills to easily cast what you have bound.
