Tobster,
You're unfortunately of an age where you've not had to do much without electronic aids. The CRP-1 or any of the other flight computers are just circular slide rules on one side and triangle of velocity calculators on the other, neither of which feature much in what you've done in maths at school I fear.
I tend to find that students of your generation usually need shown how to use a CRP-1, rather than be left to follow the instructions that come with it. The APM or AFE books are a little better, as they have pictures, but you need the book and computer to be from the same company ideally, so the pictures match. I believe Pooley's now also do a CD or DVD, which should be better again, but I've not actually seen one.
Reading peoples written instructions off pprune, will probably be little better than what you have already tried. Maoraigh1 is right, get your instructor to show you how to use it. Did whichever club you're at really just sell you it and then send you off to figure it out on your own?
Or did you just buy an "everything you need for a PPL" package off the internet? Are you still in the ATC? don't they teach you that kind of stuff there, or at the very least somebody surely knows how to work a CRP. Alternatively, being a member of the gliding club at Walney, have you tried getting someone there to show you?
The CRP-1 is pretty simple and straightforward really, nothing very complicated at all, once you've been shown how that is. You will need to get your head round some imperial units and approximate conversion factors between metric and imperial units though.