To give someone administrative access to your project or challenge, click on the "Admins" tab of the page, and click on "+ New member". Add your colleague by inputting their email address. They'll receive an invitation giving them access to the page.
This will allow them access your student teams, see their submissions, and access the Settings for your challenge. An Administrator can make changes to a project and will be contacted by students.
You can also add a "Judge" as an alternative. A Judge can view and interact with student teams, and can provide feedback. Judges cannot make changes to the Challenge itself.