Although Remington made a variety of different models, from your description I'm guessing that you have a 1920's Remington Portable Mark One.  This is a glossy black machine which has a knob on the right hand side that operates in an arcuate slot.  Moving the knob should make the typebar rest raise up, ready for the machine to be used.  I wouldn't take anything further apart until you know a bit more about typewriters.  I have seen a similar machine wrecked by someone who tried this.  Almost certainly a linkeage has become disconnected.  It should just be a case of moving the lever and manually raising and lowering the typebar rest to educate yourself as to how the mechanism works, then find where it is disconnected.  If you get stuck, try to take some clear close-up photos and post them on here so that we can help you.

To answer your questions : 1. I do not know where the missing screw is, but assuming that you have a replacement - very likely you can find a way of fitting it without too much dismantling.  2. Most unlikely.  There are a few workshop manuals around on the internet that kind people have scanned and made available, but they are largely for standard machines, and younger than yours.  Your machine would be from the 1920's.