1. Place your cursor in the post where you would like to place your image.
2. Click on the Add Media button. At this time you can Upload Files into the Media Library (make sure the image you want has a checkmark on it) and click on the blue Insert into post button. Or click on Media Library, click on the image you want and click on the blue Insert into post button.

Please note: You are able to choose the placement of the image and the size by choosing one of the options listed.