go to pictures on the top bar. At the right hand side you will see upload picture. After you click that you will be prompted to choose a file from your hard drive or use a remote picture web address.
Choose the file from your hardrive/desktop.
Then just follow the prompts.
If its just a picture you want to put in a sale thread or something, click private at the bottom.
If you want everyone to see choose public.
not enough people take advantage of these options.