Masks, of the proper grade and in conjunction with eye protection and hand protection, worn correctly and both put on and removed correctly, are effective at protecting you from coronavirus and others from you if you have it. However, these are the things that doctors and nurses need to wear which treating patients with COVID-19 - buying them may means shortages where they are actually needed.
Anything else may ameliorate the risk both to you and to others from you, if worn correctly and both put on and removed correctly. In fact anything that covers your goo holes (valved masks with no exhalation filter at the bottom of the ladder, just ahead of the bead-mask) will greatly reduce the chances of you passing it on to anyone else if you have it, especially in conjunction with gloves. They're not an absolute barrier that protects you in full, and if you put on or take your mask off like Shinzo Abe does:
... they may be almost useless even if they do stop you directly huffing it in your mouth and nose, because you're putting the stuff you're trying to keep off your face right onto your fingers, which you then use to rub your eyes, pick your nose, or yoink a bit of pork from between your teeth.
For the correct procedure, imagine that every piece of PPE has diarrhoea smeared all over the external (protective) surfaces.