There are a number of resources. I’d recommend the Security Learning Academy as a good place to start:
Another resource for good general reference and tutorials is https://developer.bigfix.com/relevance/guide/.
http://bigfix.me/ will have many examples you can review and often adapt for your purposes as necessary.
And of course, this forum can hopefully be quite useful as well (particularly if you have questions about relevance and its usage or optimal approaches).