To locate it it, use the following command :
dpkg -L package_name
Alternatively, you can search it in Unity by pressing the launcher and typing the name of the application or package you installed.
To run it as a normal user, open the terminal and type in the application name, that is, the command of the application. As an example, to run rhythmbox music player, you just opn the terminal and type in rhythmbox, and it will open.
To uninstall an application, you need aministrative priviledges, hence the need to use sudo in a command line. In uninstalling, open the terminal and type in
sudo apt-get remove application_name
and the applicaton will be removed. To remove everything that was added to the machine, including the installation folders and cache files, use :
sudo apt-get purge application_name