Posting pictures on the forum is basically a three stage affair.
If you resize the image first with "Paint" or some other graphics software and make it a maximum size of 768 pixels wide you will find it all much easier and quicker. I would also advise saving it as a .jpg extension.
Next you must upload the photo to an online storage site like Imageshack or Photobucket etc. All these are free to use.
Then you need to copy the online code for the image (link) from the site, usually says embed or similar.
Lastly you need to paste the link into your post. If you have followed my steps the picture will appear perfectly sized when you have finished.
If you want to post more than one picture just repeat the above steps.