Oh Lord, so much advice, haha. The best place to start is just browsing around the forum, but if you have any exact questions just ask. We're a friendly bunch with lots of experience
Under the area to put your post (when you hit "post reply", not on the quick reply) there's an area for "additional options" and you can attach a photo there
Of if it's on a website somewhere (facebook, photobucket, etc.) you can copy its URL and use the "insert image" button when posting.