Welcome to the QuickBooks Self-Employed family! Thanks for choosing QuickBooks for managing the transactions for your business. It sounds like you've downloaded the app onto your phone, which is a great option for keeping on top of your work on the go.
When you download an app onto a mobile device, it should automatically create a shortcut for you. It may have gone to a secondary screen rather than your main home screen, so I recommend swiping through to see if it ended up elsewhere. If it did, simply move it to where you'd like and you'll be good to go. If you're not sure how to do that, I recommend using Google to search for the instructions for your device.
Once that's taken care of, it's a simple tap of the icon and you'll be able to login to start using the program. Another way to access the program is through a browser. Here's how you'd do that if you'd also like to explore that option.