You first have to have the pictures uploaded to the internet.. They can either come off your website or be uploaded to a photo site like photobucket.com..
Once uploaded then all you have to do is copy the URL link for the picture, come to the forum here, open a post and up top of the area where you type your message, there is an icon that looks like a tree, click that and a prompt window pops up.. Paste the URL link of your picture into that window and click ok.. It will automatically enter the code for your picture..