To view your installed packages or themes, open settings with Ctrl+, and select either the "Packages" or "Themes" tab in the left-hand navigation bar. Note, the packages or themes you installed from other publishers will show up under the "Community Themes" section and themes pre-installed with Atom will show up under the "Core Themes" section.
To view information on packages and their settings, click the package name.
Browse Atom packages online here.
Downloading and installing themes follows a similar process to that of packages.
To view information on themes and their settings, click the theme name.
Browse Atom themes online here.