How can I learn about the rules of the UK, and how I can be legitimate and good citizen if I start my own small business.!?
Get an accountant, at least for the first year. They will save you far more than their fee, and will tell you everything that you need to know. They will make sure that you claim for everything that you are allowed and will keep you up to date in all legal taxation changes etc.
Go to hmrc.gov.uk they offer lots of advice on their website or over the phone and do workshops and free training