Maybe, maybe not, if you have a compact camera. Depends on model menu.
But Yes, sure, assuming you have a DSLR. If you say which camera model, we can be more specific. But the DSLR should have a flash menu, to select TTL or Manual flash. If manual flash is selected, then there is a submenu under it to specify manual flash power level.
This DSLR flash menu is only about the internal flash. It has no affect on a hot shoe flash (except for the SB-400, in which case, this is its only menu too).
No argument here, and I've learned a ton from them. I have, however, found that for some subjects, when you're really unfamiliar with it, it can often help to seek the direct, specific advice of experienced individuals. Just getting answers for a particular problem can provide grounding — a starting point, if you will. Then you can take that kernel of knowledge forward and better apply the information you can find in books, or (in this case) at Strobist or other online resources. Prior to that, there's such a wealth of information that it can be a little overwhelming. Varies with the person, of course — I learned a great deal about Photoshop and Adobe Illustrator from books, but have never been able to pick up anything worthwhile from books about 3D software, for example. I don't think that's an indictment of the books — there's just some baseline I personally wasn't able to glean from them so I could get my bearings with regard to the rest of the information they contained.