When I did my citizenship application (just two years ago!), they were phasing out NDRS and JCAP. You might contact Richmond Borough and see if that's a new PDF and they're doing JCAP again. As far as I know, the service was stopped.
You hold on to your BRP until after you become a citizen. You'll apply and submit the supporting evidence and wait. Then you'll receive a letter saying your application has been approved (most likely) and you'll be invited to book a citizenship ceremony at the local authority you nominated in your application. Once you attend your ceremony and say the oath, you're officially British (dual citizen). You'll receive a naturalization certificate, and probably a small gift to remember the day. Then you go celebrate because you did it!
Then, within 5 days after the ceremony, because you no longer need a BRP because you're British, you destroy your card and post the remains to the address contained in the letter they sent you to tell you your application was successful.