If you click on the button that says "go advanced" which is right next to "post quick reply", you will get a new screen, in the middle of the too bar, there is an icon with some arrows (run your cursor over it and it will say Image management. Click on that. Then using "browse" and you will go to your computer where you can select and open any picture from "my pictures" on your computer, then on the image manager screen you click "upload" .
Wait while it uploads, then click back to your quick reply. Place the cursor on your reply at the end of the text you have written, the go back to the icon for image manager on the tool bar, and click it, and hit "insert all" or click on the individual image that you have uploaded (shows it's jpg title)
This is how you download from your computer.
There is another way to download from facebook, or photobucket or youtube or other links that have their own URL