Diddly.....honest ?.. nobody really knows.
At the beginning of the pandemic, the Asian countries went straight to their masks, costume rather than science. In the west we said no point as the virus was so small that it passed through the mask molecules. HOWEVER, the Asian countries seemed to do better in controlling the outbreak and we,the west wondered if there might be something in this mask malarky.
Then around May/June of last year, the scientists said ah! although the virus passes through the mesh it hitches a ride on a mucus globules which can't pass through the mesh, so it would be better to use a mask.
Since then there has been arguments for and against masks, but the bottom line is.......nobody really knows.
Just do as you are told........wear them