During a fresh Debian install, you can specify the installation of pre-assembled collections of related software packages that together provide a high-level functionality, for example, Web Server. The install screen may look something like this:
If you select Web server, the install program will take care of installing the right packages for you. You don't need to know the names of the individual web server packages. The install program will install Apache2 automatically.
What to do if you have declined to install a collection, only to realize later that you do need it?
After the initial install, you can always execute the tasksel command. It brings up the same install screen as above as if you are arriving at the package configuration step in a text-based install.
$ sudo tasksel
If your base system does not have the tasksel command installed, install it like this:
$ sudo apt-get install tasksel
It is most comforting to know that you need not be perfect at install time in predicting the required software collections. You can always add a software collection using the tasksel command after the initial install.