Ding, ding (a chime 
)
To create a personal library, you need to create the folder with your OS, then steer Kicad to find that folder.
Follow the instructions in this link and you should have one or more libraries.
When you have a library, go into the Symbol Editor,
Select the Device library,
Select the correct (pin assignment) generic symbol for your FET,
Select File > Save as
Rename the symbol in the newly opened box, then scroll to, and highlight, your personal library.
Click save, Job done!
After that, open your new symbol in your project and assign a footprint from the footprint library.