1. Go to the blog article you want to add images to.
2. If you do not have images uploaded already you will need to upload some by clicking "Manage Media Items". See Here for instructions to upload images
3. In the left sidebar all your images and other media types will show.
4. Mouse over the image you would like to add and click the "Insert Image" link (Screen Shot 1). If you have a lot of images you want added instead of adding each individually you can click the "Add All Media Items" see (Screen Shot 2).
5. Once your images is placed you can click and drag it to where you want it in the article.
Screen Shot 1
Screen Shot 2