It doesn't matter whether your account is the main or one of the family accounts. All of them should sync.
There should be a sync symbol in the top right hand of your Mac front page(near where the time is displayed). It is a symbol with two arrows in the shape of a circle. Click on it to "Open system preferences", then click sync. At the bottom of the sync page, click advanced. Make sure that your computer is listed.
If all that is correct, make sure that calendar is ticked on the list of things to sync. Make sure that the calendars you have listed on your Mac are the same listed in the calendar box in Mobile Me. That was the problem for my husband when he tried to upgrade to the new calendar last night.
I'm pretty much a newbie too and I run a different OS, so that's about the extent of my knowledge.