Ubuntu – Where can I find the directory structure and important files paths explained

The complete answer is to check out the Filesystem Hierachy Standard documentation on what stuff goes where.

But in your case, if you want to know where a particular executable is (for example firefox) use

which firefox

And you will get the full path like this

/usr/bin/firefox

on the command line, you can use dpkg --listfiles packagename. For instance, dpkg --listfiles firefox. If you want to see what files a package contains without installing it, then you can install apt-file and use that.

But you really shouldn't mess with it. There is usually no reason to manually interfere with the contents of a package. All configuration files for normal applications are placed in the users home directory. You don't have savegames in C:\Programfiles\Appname\savegames, for instance. They would be placed in /home/username/.local/share/appname/savegames. That way, if you move your home directory to another machine, it keeps all configurations and user data.