After seeing the question asked many, many times on the main site, I thought it would be best to create a post on how to upload work which the community can review frame by frame.
Uncle11 has provided simple, clear instructions, making this process quite easy once you know how
1. Open a Dropbox account and use the web interface (or install their software)
2. Place the .mp4/.mov video file in your Public folder of Dropbox
3. Right click the file and choose "Copy Public Link"
4. Click on "Copy to clipboard"
5. Paste the copied link in the text of your message
That's it! :)