Instructions
Click the "Speedbook" or "Active Skill" icon underneath the "Skills" icon on the Interface Bar, or press the "S" key on the keyboard to open the "Speedbook" interface.
Select the skill you want to add to your hotkeys from the skill symbols that appear on the screen.
Place the cursor over the symbol for the skill you want to hotkey.
Press the "F" key you want to assign the skill to.
Close the "Speedbook" by clicking the "Speedbook" icon or pressing the "S" key.