Masks do work. But they're not magical. They work to catch the virus coming out of your mouth (if you're infected) and thus limit the spread. They also work to tighten the airflow you intake, making it hard for large enough amounts of the virus to get into your system.
This is even more effective with hand washing and social distancing.
AT this point, conservatives usually bring up a study from MIT about how masks don't work. But what they haven't done is read the study- it specifically says masks don't work if you're in doors and the air is Well Mixed and you stay there longer than 15 minutes.
Well Mixed has a specific meaning in science. It means that every particle in the air is equally present throughout. And if you breathe it for too long, the mask is ineffective.
Because no shit. If every breath you take has the exact same amount of virus, social distancing, masks, and handwashing won't work at all.
But that also means the opposite is true; if you stay away from an infected person, wash your hands, and wear a mask it does work.