I would like to post a photo of my car and although I am computer literate I don't know how ?????

You need to sign up with a site that hosts your photos (Photobucket, Imageshack, etc.)

Upload your photos to your photo hosting site account

Copy the direct link for your photo

Paste the link in your ride thread, by clicking the 'insert image' box (above the text box, the icon with the tree in a frame, in between the globe & chain and filmstrip icons) and paste link when prompted to enter the URL for your image.

Done.