When you are making up a post, scroll down to the bottom of the page, below the text box. There is a button that says, "Manage Attachments". Click on it, you will get a popup window with options, "upload from computer" or "upload from URL". You can browse on your computer and select whatever picture you want. File extensions that you can post: bmp doc gif jpe jpeg jpg pdf png psd txt zip.
Good luck! :tea: