in addition to what TracyCa64 have said and to make it more simple and easy
- you can create a simple word document file giving it a heading of "additional Sheet"
- the template of the text file can be as following:-
-----Additional Sheet----
Applicant name: xyz
Form title: IMM5708
Question NO: XX
Answer continued....
date from - date to - Activity......etc ( this is the headings same as in the original form)
aug2012 - sep 2014 - JOB / xyz company
Save the file and you can upload the file in the "letter of explanation" section. if you already have a written letter of explanation then mention this attachment in it and upload it along with your explanation letter. (note you can create multiple pages in word document so it wont be a problem in adding additional sheet with your explanation letter"
Hope it helps