what are the use of these products "num_observations","250m Reflectance Band Quality",obs_cov, in the MODIS data set. What does the bit no and bit combination mean in table 1 below? how could I use them to mask the cloud?

these are collected from the MODIS product description link attached below.

https://lpdaac.usgs.gov/dataset_discovery/modis/modis_products_table/mod09gq

Thanks in advance.