Project for the web - actual start and finish dates

Hello, 

I have started using MS project for the web/ new planner for a development project for a team of 10 people. I know there already are the fields start and finish date. However, I was wondering how to add fields or a way to track/report the actual start date and the actual finish date. Ideally I will like that when the user sets a task to “in progress” it automatically records the actual start date, and when the user marks it as “completed”, it will also record the actual finish date.
Thank you!