How do we put attachment into our download link?

Hey Guys! So, I just want to know how we put in attachment for our download link because what I'm trying to do is put in a attachment for a level that I'm trying to enter into the Official Level Design Contest and I really need to make the download link work. So, can you guys please help me with the attachment stuff using words and screenshots (I'm using firefox just to let you guys know)?

Uh.....attach the file ITSELF into your post?

Actually, you will not be able to submit your entry until the submissions opens. When they will be open, just make a new thread in the "SUBMISSIONS" subforum, make a description of your level, to attach it, get down the page and search for "MANAGE ATTACHEMENTS". Then, drag a file of your computer here and click "UPLOAD".

EDIT: Also, using alternate files hosters will NOT be tolerated for submitting your entry and it will be skipped.

...uh, submissions is already open?