To setup hotels combined affiliate module you need to register with them first 
click for registration :

After successful registration and account approval login to your account 
from this url :

once you logged in to your account click on " Private Branding "

now you need to create new brand so click on " Create a new private brand "

and now select option 2 " Create a simple private brand "

and now type in only fields which are described in below image 

after saving you will find out the URL of your affiliate program just copy the affiliate code and brand number see below image for reference 

now goto your admin panel and modules then hotels combined settings to paste these credentials in order to get connected with hotelscimbined 

paste your affiliate ID Brand ID and Search ID in settings page see below image 

That is all but don't forget to enable the hotelscombined module otherwise it is not going to show on frontend 
for main search box its same process you once you generated private brand click on : search boxes 
and continue to generate your search box, once you generated your search box now copy the searchbox ID and paste 
in hotelscombined settings page below affiliate and brande ID for more details about commission and revenue please read hotelscombineds instructions.