Note that the form requires you to upload one single PDF of max 8 MB containing several documents. If you are not familiar with attaching PDF files together or reducing the size of a PDF file, please note that there are several open-source PDF Editors on the Internet, for all kind of platforms (e.g. on Snapfiels or ILovePDF).
The form is divided into 8 sections. You have to complete one section before going to the next one, but you can always come back to a previous page, if needed.
In the last page, you can review all your data: if they are ok, you will be then able to submit your application.