Q170: How can I enter a booking in the name of a client?

If logged in as the administrator / moderator, you'll find the Make reservation link in the top-right corner of every checkin24-7 page. As the administrator, you won't have to fill out the required fields such as email address etc. You can also immediately mark the reservation as confirmed and decide whether you want any emails to be sent to the customer or not.

Please note that if you don't know or want to enter ANY details (such as name) it may be better to simply mark the period as vacation. This will also make the resource unavailable for reservations in the given period (vacations can also be labeled, e.g. 'reserved for family').