You can create custom fields for users. This can be found in `Admin Settings -> Users/Agents`, and then click on the settings cog icon next to +new user.
Then click `Customize user form`. This is where you can add new fields to the user, determine visibility, and whether a field is required or not. This will be visible on the user's profile.
Note: if you're doing a user import, you'll need to create the custom fields first.