All of my experience and knowledge is with semi-auto handguns.
My revolver experience is nil.  
I have been thinking of adding a revolver to my collection.  

My question is... what is the difference between frames?  I have seen K, J, A, etc.   What are the pros and cons of each frame?

Please help a revolver noob out!  

For Smiths;

J Frame - the smallest currently availible.  Typically a five shot 38 snub.  Can be had in 357 mag but don't recommend it.  

K frame - the classic Smith 38.  Six shot.  Model 10.  Also availible in 357, ie the 19/66.  Steady diet of mag loads not a good idea which lead to the

L frame.  Designed from the first for a steady diet of mag loads.  Typically a holster rig, a bit large for concealed carry.

N frame.  The big dog.  44 mag and such calibers.

X frame.  The newest.  For the 500 mag.  Big.  Expensive.