alright, if i got a nickel for everytime someone asked me to do image tags, i would have enough to buy (insert witty, expensive item here).
heres a easy yet detailed tutorial on how to do it.
so first of all, image tags allow you to enter a URL (website address) of a picture and show it on these forums. its really simple to use once you get the hang of it.
in order to start, you are gonna need the URL of the image you wanna include in your post. as an example, i will use this url:
http://www.hawaiiperformancemustangs.com/forum/Themes/babylon/images/smflogo.gifif you click that link, you will see the image, but im not interested in using that link, i wanna show what that picture looks like. its a three step process. so youre gonna need to do three things.
1) type in the opener image tag: 
2) type (or paste) your url in:
3) type in the closer image tag:
then when i post it, the url will transform into the image that the url represents. as shown below:

you can use image tags in PMs, you can use image tags in your signature as well.