Tell your story with pictures! Here is a link to the WordPress.com support page for images which contains background information on what kind of image you should upload, what the various options mean, and that it is the same for a post (on the blog) or a page (on the navigation). The most important way is to simply upload the image from your computer.
On your WordPress.com blog, you can only post videos from YouTube and VideoPress ($60/year upgrade). No private videos on WordPress.com, only publicly posted videos.