It's very easy! Just follow these steps:

1. Click on the "Browse" button;
2. Select the image in the dialog box that appears;
3. Click "Open" to select the file and close the dialog box;
4. Type a short description for your image;
5. Click on the "Join these images to my message" button below.

Please note that only are allowed images in JPEG or GIF format, and videos in AVI, MOV, MPEG or SWF format.