>>3926674it depends where you are located, in the EU I was able to find them between 30€ and 120€ in various condition. I personally bought my OM-1 for 80€ and have had trouble finding a similar deal after I realised mine was fucked.
Leading to what problems you should look for, the usual : check high speeds, check slow speeds, obvious light bleeds in the curtain, the curtain itself (make sure it's nice and flat), the cell, etc. Apart from the cell and the looks of the curtain, expect to shoot a "test roll" where you try everything, every speed, what the cell reads (does it make you underexpose ? overexpose ?). Take this with a pinch of salt, this is what I would check on an OM-1, I'm not sure what to check on an OM-2, from what I gather, it's not too different apart from the Aperture priority which I have no clue how to test, sorry.
For the dials, I advise simply reading the manual of the camera, it should even explain the basic of photography : depth of field, difference in speed, and how to expose your pictures depending on what you want to mean to picture.
I've not read any books personally, I just try to check out other people pictures and try to "recreate" them in my own environment.
Hope I was of some help anon