Hacktoberfest is a global event in October where open source projects participate and help beginners learn to contribute. HashiCorp's Terraform AWS Provider and Nomad projects are participating, inviting contributors to submit four valid pull requests on GitHub to receive a t-shirt reward. The rules of Hacktoberfest allow participants to submit pull requests across any open source project, with the challenge completing at the end of the month. To participate, review contribution guidelines and search for open issues that interest you, and don't hesitate to ask questions or seek help from the community forum. Your contributions will be reviewed within a week and provide feedback to help improve the projects.