I'm sure folks will have a more detailed answer, but quickly. To insert a linked picture, use the "insert image" button, it's the yellow button with a little mountain landscape. To attach a picture locally from your machine, use the "manage attachments" button below the reply frame. These are both for individual posts, for a sig pic, goto your "UserCP" then to "Edit Signature" and type whatever you want then use the insert image button again. You can upload your picture you want to use into the members gallery then link to that if you don't have a hosting site.
goodluck and :welcome: :twfrox: