Go to 'go advanced' mode when you type up your OP.
There should be a little yellow box right above where you normally write for posts with some mountains and a moon. Press that, and it'll ask for an image location. Find the image you want, copy its URL, and paste it in when you're asked to do so. The image should then appear.
See those arrows and the big a small a button at the top right? Press that button to mess around with different modes in how you want to view your post - depending on the mode you'll either be writing using tags or writing everything as it would appear when you submit your post.
Hope that helps!
Remember, pictures shouldn't stretch the screen! As small and as nice as possible! And don't forget character icons if you need them:
:shiek: