The Media menu can be used to manage your existing media files, such as images, audio, videos, and documents. You can also upload new files to your Media Library using Media -> Add New.
The default screen for the Media menu is the Media Library. Click "Add New" to upload new media to the library from your desktop. Once an image is uploaded, make sure that you add in some text in the "Alt Text" field that briefly describes the image in question. (See below.) Alt Text is required for both SEO and 508 Compliance.
As with other dashboard pages, you can use the Screen Options in the upper right to configure which columns are shown in the table.