CA PPM Product Documentation is available at docops.ca.com
For example, try this link:
https://docops.ca.com/ca-ppm/14-3/reference/xml-open-gateway-xog-development/gel-scripting
We're looking under Reference - XOG - GEL Scripting.
There is also a video: How to Update a Field Through a GEL Script.
In addition to the other helpful replies from our community members, we hope this also helps you.