What are those square things I see on roofs?

Those square things, sometimes round spinning things, are air vents. There is also a type that is called “ridge vents” that are not as noticeable. Also there are attic power vents that kick on and expel the air when it reaches a determined temperature or humidity level. Ventilation is very important to the life of your roof! If your attic space gets too hot, the
heat, not only transfers down into your nice air conditioned living room, but it also builds up in the attic causing the shingles to get to hot from the underside, thus they will “dry out” prematurely. It is also important to have vents in your soffits or eaves and up towards the peak of your roof. This causes the air to move passively and won’t allow heat buildup. Also the movement of air in your attic can help prevent 
condensation during extreme cold outside air temperatures. During cold snaps the cold outside air mixes with warm moist 
air that escapes from your house through attic access doors, 
bath vents, poorly insulated ceilings, light fixtures housings,
and numerous other ways, causing moisture and frost in your 
attic space. It is very important to prevent conditioned air
from entering your attic space! Excess humidity in your home 
is not desirable! Also proper venting and insulating help prevent ice dams. Ice dams can occur when it is well below
freezing, but the snow on your roof still melts rapidly. 
The warm air escaping from your house melts the snow. 
The melting snow re-freezes when it reaches the overhangs 
of your roof where there is no warm air from your house to continue 
melting the snow, causing an ice dam to form higher and higher.
 A compounding problem!