1) Create a new line by clicking the <Enter> key
2) Once you're on a new, empty line you'll see a greyed icon to the right of your cursor
3) Click the greyed to expand a tray of options:
Out of this tray, you'll select the first option which is an image icon.
4) Once selected the Media Modal will open allowing you to select an already existing image or upload a new one.
5) After you select an image click "Save" to add it to your blog post