The iPad User Guide outlines the process of pairing Bluetooth accessories - such as a compatible keyboard, mouse or trackpad - with your iPad:
Set up and use Bluetooth accessories on iPad - Apple Support
You should also refer to the pairing procedure for specific third-party accessory - which will be found within its associated User Guide.
Should you experience difficulties, this support page should help with troubleshooting:
If you can't connect a Bluetooth accessory to your iPhone or iPad - Apple Support
If you continue to have difficulties, check compatibility with iPad and seek help directly from the Keyboard manufacturer. Otherwise, if the keyboard is demonstrably compatible with your iPad, you may be able to obtain help from Apple Support.
You can contact the Apple Support Team using the Support link at top-right or bottom-left of this page. Alternatively, you can initiate and manage your support cases using the excellent Apple Support App. The App also provides direct access to appropriate support resources. If not already installed on your iPad, the App can be downloaded from the App Store:
https://apps.apple.com/app/apple-support/id1130498044
You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians may be able to provide additional assistance:
Genius Bar Reservation and Apple Support Options - Apple