as others have said, my understanding of this is that they sent both control group and vaccinated group out to live their lives and are comparing infection, hospital and death rates.
There is ongoing recruitment for a potential "challenge trial" in the UK where some will be deliberately infected, I'm not sure if it has passed ethics board yet though https://ukcovidchallenge.com/covid-19-volunteer-trials/
For good explanation of the vaccines and other SARS cov-2 matters there are a couple of youtube channels I've followed that have clear explanations and no conspiracy stuff
Medcram - https://www.youtube.com/c/Medcram/about
John Campbell - https://www.youtube.com/user/Campbellteaching