Its easy.Find a picture on a webpage that you like,right click on it, and then left click on 'properties'.That will show you the address where the picture is stored,commonly called the URL[dunno why

].Here's one I found earlier.
http://www.cummins.pwp.blueyonder.co.uk/custom.jpg
if you click on that link ,you will see the picture.To include it in your post ,you have to code it in using HTML code[dunno what that stands for either

].HTML is a set of instructions set inside these []brackets.The basic code uses a three letter instruction in [brackets] that is included immediately before the task that you are doing.Immediately after the task you need to close the command with a slash,like[/brackets]
For adding pictures,you need to use [img] code,like this.

.
obviously,you can't see the code that I used to do that,but if you click on the 'reply with quote' link in the bottom right hand corner,you will be able to see how the tags work.
Any poroblems,feel free to ask!