Most optional features in Emacs are grouped into packages. Emacs contains several hundred built-in packages, and more can be installed over the network (see Packages).
To make it easier to find packages related to a topic, most packages
are associated with one or more keywords based on what they do.
Type C-h p (
finder-by-keyword) to bring up a list of
package keywords, together with a description of what the keywords
mean. To view a list of packages for a given keyword, type <RET>
on that line; this displays the list of packages in a Package Menu
buffer (see Package Menu).
C-h P (
describe-package) prompts for the name of a
package, and displays a help buffer describing the attributes of the
package and the features that it implements.