Its just an acient secret society. Those that are part of it usually get special business deals from the other members, and Ive heard of people being turned down for jobs because another less qualified guy that was a mason got it. They tend to help each other out and identify themselves to each other with code phrases. For example "is this a Square Deal?" is in refrence to the Compass and Square, their symbol, and means that the deal is only given to those that are masons.
Some belive that the foudning fathers of America were Masons. IF you look at a over head map of washinton dc there is a clear Pentagon, also a Square and Compass symbol made by the roads around the capitol and the white house. Also a Visica Pisces is visible around the Washington monument (which is also a oblisque, in refrence to the Eqyptian heritage of free-masonry - theres a reason that its there, its not random). Most everything that is built by governments or big business have a symbol from freemasonry hidden in plain view.
As far as their motives as a Secret Society /shrug. By in large the average free mason is just there to drink and socialize. its the upper levels that see the benifits of the money that flows in from donations or fees from the lower levels.
Honestly, I have a hunch that these secret societies are all going to disappear over the next 30 years. Kids these days just think they are silly, and the 'secret' is out there on the internet for anybody to find. (pssst, the answer is "More Light")