The follow on mode functionality allows for a different sized set of areas for the first page of a template, compared to the rest of the pages that the template will produce. This allows for example, a bigger header area on the first page.
To set this functionality on, simply select the Follow-on Mode checkbox and the follow-on tab will then become available.
The first mode, and the follow-on pages allow for completely different sizes of all areas, other than margins and the Scale. The scale must be consistent between the two tabs, so changing this on one tab will also change it on the other tab.
Note that the area used is also different between the two tabs so should be checked to make sure that all space is used as required.