Aptitude is preferred, but other approaches can be used if desired.
First, update the package index. The package index is essentially a database of available packages from the repositories defined in the /etc/apt/sources.list file and in the /etc/apt/sources.list.d directory.
sudo aptitude update
Now install the package.
sudo aptitude install package_name
NOTE:APT keeps a copy of each downloaded .deb file in the directory /var/cache/apt/archives/.
In case of frequent updates, this directory can quickly take a lot of disk space with several versions of each package.