Developing an X-KeyPad configuration from scratch can be an involved process and has a learning curve. The first thing to do is watch some of the tutorials. They will give you a good sense of what is involved.
https://stickandrudderstudios.com/x-keypad-tutorials/
The next thing to do is to see if someone has done a configuration for the aircraft you are interested in. Browse the list of community-supported X-KeyPad configurations.
https://forums.x-plane.org/index.php?/files/category/187-x-keypad-configurations/
If you need further assistance check out the X-KeyPad text channel on our Discord server:
When I’m available I’m happy to hop on a voice channel with you and help out.