How do I get a keyboard on my Apple Watch

You need a watch 7 or higher for Apple’s keyboard. For lower, look in the App Store.

Ellamay12 wrote:

I tried to download it from the Apple Watch app but I need WiFi to download it

Apps are downloaded from the App Store, and some kind of internet connection is required for that.

Get apps on Apple Watch - Apple Support

your signature suggest you have an SE model it does not seem to support the keyboard

How to access and use the keyboard on your Apple Watch (androidauthority.com)