1. log in to your control panel at https://panel.wepwawet.net/
2. Go to My Servers and press on the server you want to add them to
3. Under Server Management select the Sub users tab then click Create New
4. Put your friend's email in and select the permissions you want them to have.
5. Tell your friend to look at his/her email for something titled 'Account Created'
If this doesn't work, please send a password reset mail to the user (click here)