I'm concerned that you're over your head, unless GM means something other than general manager. The restaurant needs to bring someone in who knows numbers and you do not seem to be a numbers guy.
The basics of accounting seem to be missing from your skillset.
Revenue minus expenses equals profit. You don't know WHAT your expenses are, so without knowing that, you have no way of determining profit (or loss). You need to determine what your costs are now, look for ways to contain those costs, if not reduce them, and budget going forward. However, I'm afraid you're over your head here.
The fact that you chose "owner/operator" over "restaurant manager" for your level, seems to indicate that you're more interested in the titles and don't really have the right experience. An "owner/operator" means you OWN and manager the place. I don't mean to be rude, and some of the comments above mine do seem to be more interested in picking than helping. However, we're all getting the "vibe" that you're not to the point of being ready for "guidance" as much as needing basic training. If that's the case, you need to be honest with the owner that you're over your head. Perhaps the owner is willing to invest the time necessary to train you, but for now, you're simply blowing the guy's money if you can't even determine what your expenses are.