Did you want to post a picture of a tiny bit of paper with a corner folded down? If yes, you did fine!
If not, you size your image appropriately (I find min frame length of 400 pixels, maximum 800 pixels is about right .. ish), then upload it to a picture sharing site - Photobucket, MyAlbum, etc..
Get the link code (might be called image code or something) for the pic from that site, copy and paste it in your post. If the line of code doesn't already have 'img' and '/img' (each with a pair of [] ... which I can't type because it will try to post an image in my reply) either side of the line of code, then add them. If it does have them, leave it.