When you select 'ask your question' a box will appear and it will ask you to write your question. Underneath the text box you'll see a 'pi' sign and an 'omega' sign and next to that you'll see a paperclip sign. Click the paperclip sign and then choose the file/s you want to attach.
I have attached a docx (document) if you don't get what i mean.
Hope it helped :)
