VAT registration cut off is 81k so you dont have to even bother thinking about it.
Basically, if you register for VAT (can do it regardless of gross income, but have to over 81k), you claim back the VAT on your purchases so it's not paid twice. Currently you can imagine you buy a product with VAT and then sell that on to the customer with VAT (although it may not be that explicit).
Of course, if you sell products exempt from VAT, you dont have to register.
google VAT registration for the HMRC website, it covers most of the ground you'll need.
Only certain products/services include VAT so you can't just take off 17.5%. You're probably better of registering as a company and registering for VAT so you can get the tax benefits. i.e. VAT reclaim on fuel for "business trips", expenses for daily sustenance, business purchases etc. You can effectively pay <5% tax if you're smart and have a friendly accountant.
Good luck!