First, you need to upload your image to a service like tinypic or imageshack. Then, you can hotlink it by using the tags before and after your image url.
"[ spoiler=Title ] [ /spoiler ]" to hide your text or image in a spoiler
[ b ] [ /b ] is for bold, [ i ] [ /i ] is for italics, etc. When making a new post, go to advanced and you should be able to find all of the settings you need.