How do I use Groovy script in Jenkins pipeline?

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Tags

1. #manually
2. #based
3. #groovy
4. #source
5. #script
6. #control
7. #reads
8. #bring
9. #section
10. #instead
11. #clicking
12. #jenkins
13. #jenkinsfile
14. #plugin
15. #pipeline
16. #checked
17. #through
18. #click