If you want to add additional modules for Apache extension. You can install additional modules, for example, you can install module to add support for PHP, and the likes.
Run the following command to see a list of modules available for Apache:
apt search libapache2-mod
The following command would output several apache module packages, e.g libapache2-mod-php7.2 (this adds PHP7.2 support), so, to install the package, you simply run the following command:
sudo apt install libapache2-mod-php7.2
By default, installing module package is not enough for it to work in Apache, to view a list of modules that Apache has available, use the following command:
These are the built in Apache module, and are already enabled, to view a list of all modules that are installed and ready to be enabled, you can run a2enmod, it would show you the installed module, and ask at the end of the output if you would like to enable any of the module.
Your choices are: access_compat actions alias allowmethods asis auth_basic auth_digest.... Which module(s) do you want to enable (wildcards ok)?
If you know the module you want to install you can type the names, alternatively, you can give the a2enmod command a module name as an option, it will enable it for you:
sudo a2enmod php7.2
Most of the time, the major modules would have likely be enabled for you, if that is the case, you would see the following output:
Module (name) already installed
If the module isn't already enabled, it would enable it, and you would be asked to restart it, this way, the module will take effect.
To disable a module, use the a2dismod command, e.g
sudo a2dismod php7.2
Restart fo the changes to take effect.
If you are installing a third party module, you would need to get the name of the required module for the third party application doc.