Here's some basic functionality offered by APT:
install/remove a software package (requires admin privileges):
apt-get install/remove pkgname
display basic info about a package
apt-cache show pkgname
display packages whose names and/or descriptions match the search pattern
apt-cache search pattern
Here's a usage comparison with other package managers.
[note] APT keeps a log of some of its activities at "/var/log/apt/history.log".