Look near the top of the page and you will see a "Gallery" tab on the left...
Click on it and it will bring up another page and on the far right near the top there is a tab "upload pics"...
Click on that and it will bring up a page that lets you browse your computer for pictures...after you have selected the pictures, look below it and hit the upload/submit tab.
Then when your pictures are loaded, you can copy the "BB" code and paste it in your thread.