To get to the App Library, start at the Home Screen and then swipe left until you reach the end of your Home Screen pages.
Here, you will see all of the apps that are installed on your device.
You can tap on the search field at the top of the screen to search for a specific app, or you can scroll through the alphabetical list to browse all of the apps.
When you find an app that you want to open, just tap on it and it will launch.