N95 masks are good at reducing particulates that go into your lungs. I use them at work all the time.
A couple things to remember.
1) When you buy them, they will always say N95 on them. If it doesn't have a rating, it is a comfort dust mask, which are junk.
2)
They will always have 2 elastic bands. You put the first elastic band (bottom one) over your head, slide it down to your neck, position the mask in place, and then slip the second one on to your head, and then pinch the nose piece. Do not just use the top one leaving the bottom to dangle. That is useless, though I see people do it all the time because it is more comfortable.
3) Having a facial hair will reduce their effectiveness.
4) Wearing them will require you to breathe
slightly harder. For the vast majority of the population, this won't be a problem. That said, if you have some underlying difficulty breathing, you may have issues. If you are unsure, I'd say try it in a resting situation and see how it goes, and then work up to more physical activities. I wouldn't start running around outside in 95 degree weather doing calisthenics. Keep in mind, I'm not a doctor.