When you are posting a reply you should see some buttons above the text box.
B = (bold) I = (italics) u = (underline) etc.
If you click the Img button you should see something like [im g] [/img]
Post the link to the image you want in between the brackets and it should give you what you are after.
I may not have explained it brilliantly but hopefully that helps!
So, for example, if you wanted a picture of the best player in the Championship you would do it like this
