First Off, you need to host your images. I suggest you use these sites, the first two are owned by me - and i'm willing to offer 24/7 support for free. ImageShack is a competitor of mine, but also pretty good:
NEVER, I repeat, NEVER use ImageCave, MyOnlineImages or any other site not on our list. If you submit a tutorial using any of those free sites - submission to sites will be delayed or denied (they limit bandwith).
Now for the posting part, to post an image use this BBcode:
If you wish to post an image with a link, use this code:Code: