Navigation Drawer and Fragments best practice

I am going to use Navigation Drawer in my app. I have read about most common approaches of building such apps, a lot of people suggest to change only framgent while selecting different items in navigation drawer. So instead of openning new activity it is better to change fragment of current activity ? Am I right ?

The problem is that I have main activity with two fragments now.

What is the best practice to follow in this case.

To open new activity on item click in navigation drawer ?

To use nested fragments, because my activity already has 2 fragments, so maybe to create some wrapper fragment to nest these two fragments or more if it will be another page.

Please suggest what is the best practice to implement this design pattern in my case.

Thanks in advance.