A second space is where you spend most of your time that is not at home, like work or school.
A third space is everything else. Shops, restaurants, parks, etc.
The issue that young people are facing is that there isn't really anywhere they can exist that isnt at home or school. Communal spaces where young people are allowed to spend time, especially places where there isnt an expectation to spend money constantly have been eroding away over the past 30 years.
It's not a coincidence why most pre-2000 teenager-focused media has the mall as a main setting