OK when you open a past page look for the small button that says "host an image" when it is opened you will click on choose file. Find your picture on your computer and click on it, next in the new window that was opened to show you the pictures, click open.
This will add the link into the "host an image section. From here click "host it" the window will cahnge giving you three choices, "Thumbnail" "Full Image (I think)" and "URL" copy either the Thumbnail or the Full Image and past it into you post.
The hard part is the Host an Image page is kind of in the way you have to work around it.
I like to preview my my post first, when you do this the window will go away and then you can make changes if you need to. I know that seems boring and lot to do for a simple picture but once you get the hang of it it will be easy.