to expound upon that, once you have uploaded your images go to the top of the website and click the gallery tab. Once that page loads, on the left navigation bar select my gallery. Here is where you will find the images you have uploaded. Click on the image you want to post in your message, when it loads right click and find the source for it. it will look something like "http://www.derkadkera.com/1923.jpeg" copy this, and go back to the post you are currently working on. On the top of the form field box you're typing in, select the button that looks like a picture. When the box pops up to enter the source of your picture do so and you're done.
hope that helps