If you're new to Android, the term launcher might be confusing. The launcher is basically the home pages and the apps tray. It's the home of your phone.
Your device will come with a launcher in place, that of the manufacturer. If you don't like it and want a different look to your phone, it's really easy to switch to an alternative and there are loads in Google Play.
When you install a new launcher, the original stays on the phone so you're not losing it, you're just telling the phone to use a different launcher instead, meaning you can escape from the looks of Samsung One UI if you don't like it, for example, and have something a little more unique.
If you want to get closer to Google, then the Google Now launcher will give you access to more information with a swipe and give you generally a clean Android look and feel.
If you want more control and customization - as well as the ability to emulate some of the latest features from some top Android phones - then there are few launchers as capable as the Nova Launcher. The possibilities are truly endless.