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.

Packages

1. Press Ctrl+, to open the settings tab
2. Select the "Install" item on the left navigation pane
3. Ensure the "Packages" button is selected in the top right

4. Use the search bar at the top to find a package (ex. file icons)
5. Click the Install button to download and install the package

To view information on packages and their settings, click the package name.

Browse Atom packages online here.

Themes

Downloading and installing themes follows a similar process to that of packages.

1. Press Ctrl+, to open the settings tab
2. Select the "Install" item on the left navigation pane
3. Ensure the "Themes" option is selected by the search bar.
4. Search for a theme (ex. atom-sublime-monokai-syntax)
5. Click the install button to download and install

To view information on themes and their settings, click the theme name.

Browse Atom themes online here.

apm is Atom's native package manager. It allows the user to manage packages and themes without having to initialise Atom itself. apm comes with the official installation and is automatically added to %PATH% if you're on Windows.

To use apm, go to Command Prompt and type

$ apm <command>

Here is the list of what you can do with this package manager.

clean, config, dedupe, deinstall, delete, dev, develop, disable, docs,
enable, erase, featured, home, i, init, install, link, linked, links, list,
ln, lns, login, ls, open, outdated, publish, rebuild, rebuild-module-cache,
remove, rm, search, show, star, starred, stars, test, uninstall, unlink,
unpublish, unstar, update, upgrade, view.

For example, if you want to do upgrade all packages from atom:

apm upgrade --confirm false

Or if you want to install a specific package:

apm install <package_name>