How do I create a hackathon?

Login to your Devpost account and hover over your profile image in the top right corner. Select "Manage hackathons".
On the next page you can view all the hackathons you have created. To create a new one click "Post a new in-person hackathon".
Once you enter the name of your hackathon and the date you want hackers to start submitting click "Create my draft hackathon".