In order to add another user to have access to your control panel you need to do the following steps.
Go to https://minecraftserver.net/panel (Don't log in)
Click "Register here" if you don't have an account yet.
Create an account for that user you want.
Once done this log into your account then click users, after that type in the users name you want to have control and give them the access you wish for them to have.
Please note that we don't suggest giving everyone control to your server unless you trust them as they could delete all of your files if you give them that access.