Insert value from checkbox into database in php

What I want to do: when the user registers on the website they should check one of two checkboxes. Depending on what checkbox they chose the pages will differ once they're logged in.

I have tried several guides on how to do this but I can't seem to make it work. I have uploaded the important files to GitHub if someone would be kind to look at it. The checkboxes are in register.php and the column in my database where I want to insert their value is called usersType.

Github: https://github.com/Agnes2774/Registration