Removing pages from automated menu

Hi
I wondered if someone could point me in the right direction, I’m not sure which keywords to search for my issue:
I have installed a simple “CMS style” wordpress site, with a theme design that only has room for about 4 pages titles in the horizontal navigation menu. My site however requires more pages, and some minor ones like contact, about us etc, that need not be in the horizontal main nav bar.
It seems however that each and every page gets listed in my nav bar, resulting in some being truncated and some not appearing at all.
Could I add a “property” to my pages to indicate if they must appear in that looping menu, or would there be a plugin to do that as I guess my case is not rare ? Obviously I could use parent pages but this is not really logical in this case. Thanks WP gurus !