New manager - any tips?

I’m head of marketing and recently welcomed a junior specialist to my team, making me an official manager for the first time! I’ve worked with freelancers before, but this is my first experience managing a full-time employee.

Any tips from experienced managers, particularly those who’ve worked with juniors? How do you balance giving them enough structure to do their job while also leaving room for them to take initiative and make it their own? Also how do you deal with situations where they challenge you but you’re 100% confident your suggestion/project/process is the right thing?