Go to the member introduction forum. There is a sticky there which describes, step by step, how to put a picture on this site.
You actually need to get an account on one of the picture hosting sites like "Photobucket". Go to photobucket.com.
Photobucket membership is free. You upload your pictures onto Photobucket. Any time you want to put one of your Photobucket pictures into a thread on this site, you go to Photobucket, copy the pic you want and then paste it here in your thread.