We actually don't have a section exclusively for newbies to the hobby. There is a search feature (Google Search) at the top of the page that can offer you help and advice with any subject you can think of. Just use key words like, 'chain tensioner' and you'll find plenty to read.
We do have other members from the UK so maybe one of them will chime in with some input as far as your legalities are concerned.
Good luck, ride safe.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"