Keyboards can be installed from the Google Play store the same way you install new apps, but keyboards normally have to be activated before they can be used on the device. See How to install and activate a new keyboard on your Galaxy S10?:
- Launch the Google Play Store application.
- Locate the keyboard app you intend to install. Popular keyboards are SwiftKey, GBoard, and Grammarly.
- Click “Install.”
- After installation, click the keyboard application app you just downloaded to launch it.
- Adhere to the instructions in the app to activate it.