You can access the Media Manager through the Control Panel, or by going to Site > Media Manager.
The Media Manager is a very useful for uploading or deleting files in the <joomlaroot>/images/ directory on your web server. You can upload new files, delete existing ones, and create sub-directories. The Media Manager offers two views, thumbnails, and details view. The first will show a much smaller version of the original file (assuming that is an image), the second (details) will show the file name, dimensions, and file size. There is also a handy 'delete' button next to each file.
At the top right you will see the toolbar:
The functions are: