Firstly, you must login. If you have not registered yet, just click the "Create new account" link. Then go to the Photo Gallery. At the top of the page you should see a "Your Album" link -- click it to get to your album. Now you will see an "Add a Photo!" link, so click that. You will also see on the left some other options such as "Add Album". Now you have a form where you can browse to select files from your computer and upload them on the website.

If you are doing a lot, I recommend you click the "Upload Applet" tab which is a bit more user-friendly to add many photos (you can just drag and drop them). Then edit the captions and descriptions as you want. Any that I particularly like I'll create a link to in the other albums so that they can be seen there too.

Note that they may end up being watermarked with Jitsu Canada, just so other people don't steal them.