Tutorial on setting up sites in MU network?

I’ve been trying to set up extra sites in multisite for a week now and the sites are showing up under my sites in the admin drop down, but when I go to the site or the dashboard, it says they’re not found. My web host tried to tell me buddy press (which is my main site theme) is not compatible with multi-site. I think it’s just because they can’t figure out the problem. Is there are tutorial on how to set up secondary sites once you have MU set up and working with your main site? I’ve got to be missing something here.