To attach images to a post, click on the "Additional Options" link below where you type your message.  This shows an "Attach" box and you click the "Browse..." button to select a file to attach.  If you want to add more images, click "(more attachments)" and more spaces will be added for you to add pictures.  You are limited to 4 attachments per post, and must add up to less than 256kb.

To make your images smaller use your favorite image editing program to shrink them down.  I recommend a size no wider than 640 pixels to fit comfortably on this forum.  Save the resized image as a JPEG image and you will easily fit 4 attachments in 256kb.

Hope this helps - let me know if you need further help!