Horological Meandering

Hey I was just given a GP watch by my father. It is at least 50 years old. I cannot remove the back of it, how do I do that. Also how can I find out what it is worth. Thanks

. . .ahem, sorry for being facetious. OK, in general for vintage watches original condition is the biggest priority; a good condition, clean, original dial, unmarred hands, and a case that is neither ill-used nor (badly) repolished will all increase the v... 

I appreciate your time writing that! I shall act on your advice and join the forum now! All the best Lawrence