Give or take the Double Ring and Single Ring variants, that one is the oldest of the Gillette safety razors with a patent going back to 1904. Still made well into the '20s, it had a good run.
As
@TobyC says, take your angle from the cap. If you get straight lines in your lather from the comb, angle back towards the cap. The cap bends the razor blade and that is the ideal angle to follow. The comb is (again) only there to stop you beaching the blade into your face and it's open, because folks back then did not shave as frequently and so it mitigated against clogging up.
As with the blades, no reason to hold off using it ...
When I first came to traditional shaving, I anguished over my razor choice (like there has to be a choice) and bought the Merkur 23C. I think I managed a mere handful of shaves before I was using a Gillette Parat, a Gillette New and a Gillette Red Tip. Very quickly thereafter I was onto pastures new with the 1912 and single edge shaving ... and everything (and I mean everything) else over a two or three year period.
For me, the joy of finding and collecting vintage took precedence over my desire to actually shave with much of what I collected. I have shaved with just about every model of razor that I have (whether or not it even had blades available, pressing anything into action - usually an injector blade), but far from shaved with every actual razor that I own or have owned.
If that's to be your thing, happy collecting! Loads of knowledge, advice and expertise here ...
