First and foremost, you'll have to register in the gallery software, registering here, unfortunately, doesn't automatically register you in the gallery.
Once registered, you'll see a menu on the left side of the screen. Around the middle of that sidebar you'll see the MENU area. The last link in that menu is "Upload Photos".
Choose the appropriate album, then drag or select images to upload.
All uploads must be approved by me. So PLEASE add a good description, and specify whether your photo can be used for commercial purposed, otherwise it will be subject to the non-commercial license.
As usual, you must own the copyright to the image, or be prepared to provide proof that you have permission to distribute. Can't just say "Dude said I could upload it". If someone comes along and says an image of theirs was uploaded without their permission, I'll investigate as best I can. But if I can't dispute their claim, the image comes down.
Please post a new topic here if you have any questions.