If you are talking about creating a gallery to post your pics, click on "User CP" near on the blue bar near the top of the screen. Once that page loads, click "Edit Gallery" on the left side of the screen. Next, you will have to click "Create New Gallery" and then just follow the instructions.
If you are talking about posting pictures in your messages, then you can either copy and paste that picture in, or click the button above that looks like mountains with a sun. If you hold your mouse over it says "insert image". You will then be prompted to type in the Address of the picture. Good Luck!