Every Education doc should be uploaded as one file, every passport doc as one file. There are multiple places to upload employment docs if you have different employments, so you should combine every individual employment document i.e ref letter, payslip, biz card etc and upload as one file. You should save all of them to a PDF file and use this website http://smallpdf.com/compress-pdf to compress the file so that it is not too large.
All the best.