Your question is about the presentation of evidence, and in this case, your bank statements...
You have completed the online application and you have scheduled an appointment for your biometric enrolment at a VFS.
However, I am confused as to when or how I am supposed to do so?
You should print out your application. The online form has a button to click to accomplish this. Using A4 is preferred, but they are happy to accommodate North American applicants who use 'legal size' or 'letter size'. Now you have a stack of paper.
Order your bank statements (originals please) in descending order by date. Place these underneath the 'stack of paper' you created above.
Take your other evidence (originals please) in descending order by priority and place these at the bottom of the stack.
Make an enumeration of EACH AND EVERY PIECE of evidence and add it to the 'comments' section of your application. If you are using the new forms, you will have 'locked' your application and will be unable to do this (tell your friends not to make this mistake).
So you have to make a 'Transmittal Letter' and hope that the VFS does not discard it. A transmittal letter is a print out that gives your name, nationality, date of birth, passport issuer and number, and GWF number. Then it itemises each discrete piece of evidence. Put this on the top of your stack.
Take all of the above to the VFS when you enrol your biometrics. They will know what to do next. However because you are a T5 applicant, you may have to post your application directly to Sheffield (or Croydon), so put the whole shebang (including your biometric receipt they gave you) into an envelope and post it.
NOTE: There are no rules or regulations governing this aspect of the process. There are no authoritative links to provide, just a few pathetic threads on internet forums. This answer is based upon pure reasonableness.
NOTE: UK solicitors will always (repeat always) prepare a transmittal letter or include it in their cover letter. It is part of the polish and know-how you pay for when you instruct a solicitor to handle your application.