Question: How do you know what certain packages are called

Answer

On Debian there are multiple ways to find out things about packages. Most of the ways are done via apt-cache, you can search for packages: apt-cache search. If you have aptitude installed, you can also search with aptitude: aptitude search.
If you want to know what packages contain what files, you can use apt-file: apt-file search. apt-file isn’t installed by default, so you need to install it first. And if the file already exists on the system: dpkg -S. With dpkg you might need the real location of a file, so use: dpkg -S $(readlink -m /path/to/file) to get better results.

If you want to know which packages are installed by other packages you can look at apt-cache depends for all the dependencies and apt-cache rdepends for all the reverse dependencies.

To know what a package brings to the table: apt-cache show.
If you have multiple sources configured, often seen with those who run Debian testing/unstable you can configure apt to only show one version:

# /etc/apt/apt.conf.d/99-apt-cache
APT::Cache::AllVersions "0"