Once you have your own account you can create a group, and add your guests to it.
You can do this by clicking on My group in the My Account menu or directly from your profile screen using the Create Group button.
You will see a screen where you enter the group name and then the list of members which will initially just have your name as the primary member.
To add a non member guest you click on the Green [ Add Guest ] button and enter your guest's name and email. A guest account will be created for them.
If a member has created their own account and is also your guest eg where a couple are both members, or a parent and child, use the yellow [ Add existing user ] button instead. You need to enter their username, which will generally be firstname.lastname.cc where cc is their country of residence as a 2 letter code.
Once someone has an account and is in your group, you can register them for events, as well as yourself and have the event costs added to your cart.