Hacktoberfest is a month-long event in October organized by DigitalOcean and hosted on GitHub that encourages contributions to open source projects. Participants can engage by opening pull requests to fix bugs, add features, or enhance documentation in any open source project. First-time contributors can refer to a guide on contributing to open source, and those who complete four pull requests by the end of the month receive a t-shirt as a reward. Participants are encouraged to share their contributions on social media using the #hacktoberfest hashtag. More information can be found on the Hacktoberfest website.