Simply hit the Submit button at the top of the page!
Depending on the type of media you’re submitting hit the drop down to change between photo and video!
For submitting youtube videos after selecting the video option you should just be able to paste the URL of the video in the embed box. If that doesn’t work you can grab the embed code from any video site and stick it in there!
If edits need to be done your submission credit may be lost (darn you tumblr!) so be as precise as possible!