One question that comes up often is what are the differences between the Justice Society and the Justice League. The JSA is not only the first team at DC, it is the first historically.
The teams are much alike. The JLA was inspired by the JSA. However, in the current series, there are several differences between them.
1-The JSA is much more a family unit of legacy characters. There is less focus on DC big guns in the membership, though the JSA has historically had some major DC characters, such as Dr Fate, the Spectre and Starman (I'm trying not to include obvious majors such as GL, Flash and Hawkman).
2-The JSA members are usually former characters of what was once Earth Two before the Crisis. Classic Earth Two characters such as Black Canary, Wildcat, Powergirl and Hourman have had strong ties to the Earth Two history of the DCU. It would appear that the tradition continues with Earth S and all the Captain Marvel characters.
3-The JLA is the first front of defence on Earth. The JSA is probably the second and more US based.
4-The JSA has trains new heroes in house, instead of sending them to Young Justice, like the JLA.
5-The JSA characters are more likely to die and go through nonreversible major changes than the JLA guys.
6-The JSA keep a watch on the other teams.
7-The JSA is not loose knit. Members are voted in just like in the JLA. Some members, such as the older guys (Flash, GL, Wildcat and Hawkman) don't show up as much, because they are semi-retired. Although they would listen to their field commander in battle, they are a so experienced that they there's no need to tell them what to do.
8-The JSA probably train as much as the X-Men or the Avengers.
9-Many live in the JSA HQ. Others come and go.
10-Sand, is the financial backer. He inherited the fortune of the Sandman, a founding member.
11-Many JSA members have publicly known. Some are less. In general they focus less on hiding their secret identities. Sentinel still protects his identity, though, most people must know about him. Some characters without identity are, Hawkman, Hawkgirl, Sand, Hourman, Jakeem, Wildcat, Starman, Flash, Dr Fate, Black Adam, Atom Smasher, Black Canary. Mr Terrific and Dr Mid-nite are known to many, it seems.