Look inside the Project Setup pod. There you will find a Master Pages folder. Right click on this and create a new Master Page which is opened as a topic tab. Change this as you require and save it. Next you will need to assign this to the appropriate topics by right clicking on them and selecting your Master Page in the properties. If you are assigning it to multiple topics, you may find the Topic List pod useful as you can multi select your topics and assign the master page in one go.
Wow, this is a case for screaming "RTFM!!!!!" into my own ears.
Then again, I can perhaps be pardoned by the fact that due to Quebec regulations, Robohelp has to be installed in French, so the term "master page" didn't appear anywhere. The french term is a bit more vague.
As I am currently on vacation in the south of France I'll let you off
Out of interest, what does it display in French Canadian? "Page Maître" would seem right to me. Maybe it is different depending on the regional French being used.
Actually French (Canada) has it down as "Pages Principales" (main pages). Had it been Pages Maîtres, I would have recognized the terminology.
If you think the terminology is wrong, the chances are that other French Canadians do too. I'd submit a change request to see if you can get it changed in a future release. You can do so at Adobe - Feature Request/Bug Report Form
Hmm. Do Master Pages only let me change the contents of the <body> by adding new HTML?
Am I missing something, or is this a limiation of master pages?