[Animats]

You can install F-Droid, which lets you download open source apps.

At startup, there's an option to register with Google, which you can skip. It will keep popping up until you disable the "Google one-time startup" app. Also, without a Google account, voice input and voice dialing won't work; Google deliberately broke that about two years ago. There are alternatives, such as Samsung S-Voice, but it's hard to find a good one that isn't just a front end to Google's system.