did not receive instruction book on how to use i phone 8, help!

The Home screen should open when you enter the passcode or open with your fingerprint. Here’s a good place to start→Set up your iPhone, iPad, or iPod touch - Apple Support. There’s a link at the end for more information and guidance.

You can get also get the full manual by opening the Books app on your phone and downloading it to your phone, or at this link→iPhone User Guide - Apple Support

Hello. On your iPhone 8 you can return to the home screen by clicking the circular home button at the bottom of your screen.

If you need help with using your iPhone, you can reference the user guide available here.