1. Make sure that your pic is not too big i would say a max of 20kb
2. You need to upload your picture somewhere on the web, there are many sites online that allow you to to create albums and store you pictures eg: www.fotango.com is one of them.
3. You need to get the correct link address to your picture.
4. When you create a new post and you are ready to insert your picture you have to click onto the IMG button this you find just above the typing area box, when you click on IMG another small box will appear where you have to paste in your link address http/ etc to your picture, when you have finished your post you then click on submit post or you can preview it before submitting.