To upload stuff to the server here is easy: when you're replying to a post, scroll down a little until you see a button that says "Manage Attachments." Click that, and you'll get a little window with text boxes in it. Click Browse next to one of the boxes. Another window will open, and you can navigate to the file on your computer that you want to upload. Click the "Open" button; the second nav window will close, then click the Upload button on the Manage Attachments window.
That's all you have to do. If the pics you're trying to upload are bigger than 699 x 699 pixels in width and height, they're too big, and you'll get an error message, so just make sure they're smaller than that and you won't have any problems.