In the case you have created your sellers who tend to call your or send an e-mail to book as an affiliate to keep track of their bookings, you can manually add the affiliates to the bookings in the booking process both via Booking Desk and New Booking.
In the booking desk there is a field titled "Sale Source". In that field you can write the name of your affiliate, after two letters the field will suggest names to you. Select the correct affiliate. If the affiliate doesn´t exist yet you can create it here in the booking process. Just note if you do that you have to select "Contracts -> Affiliates" afterwards and add the commission to the affiliate, given that the affiliate should get commission.
In new booking there is a blue field at the top of the screen where the affiliate can be selected. Note that the affiliate has to be selected before you start the booking process. If you add it later you will loose the information you have added. In that field you can write the name of your affiliate, after two letters the field will suggest names to you. Select the correct affiliate.