To edit a contact, go to the contacts module and use the column filters to find the contact you would like to edit.
Click anywhere along the row of the contact to bring up their profile.
Select 'Edit contact'. You can edit all the details you hold for a contact and give the contact Tags, Booking responsibilities and Administrator roles.
The edit contact screen is also where you can 'Manage custom tags'.
Here you can create custom tags which can be assigned to any contact.
You can then use the Tags column in the contacts module to filter your list.