The contractor will make the tax deduction for you (the subcontractor). Best to register for it as the deduction can be defaulted to the higher rate (30%) if you don't register. Otherwise it will be 20%.
The HMRC site will have the CIS340 handbook, which has a good overview of what work will fall in and out of the scheme. Think it starts on page 90-odd.
I've only really done work from the contractor side, but can offer advise from that perspective if needed.
"The things you own, end up owning you."