Please put your submission in a folder with a distinctive title, perhaps your name. This folder can contain html files, dmg files, or anything else you like. I'll put the folder on the web.
Place a special text file named "ReadMe" in the folder. I'll extract this file from the folder and use it to add your contribution to the User Contributions page. The ReadMe file should contain four paragraphs with the following information:
Send email with your contribution to the address at the bottom of this page. In the email you can describe the contribution if you like. The email should conclude with a dmg file containing the submission folder.
As an example of all of this, consider the TeX-Scripts provided by Claus Gerhardt. His folder is named "Claus_Gerhardt" and contains a single file named "TeX-Scripts.dmg". The first three items of the ReadMe file look like this: