I'm reading a book called "Meteorology Demystified." It's pretty good, but like every other book on weather I have read, it fails to explain to me why some air masses are high pressure and some are low.

For example, it says that there are low-pressure regions at the equator and and 60 degrees north and south. The equator would be a hot region and 60 N and S would be cool to cold. So how can they both be low-pressure? Can somebody explain this to me?