Steelbook information for beginner collectors

[Cell]

I'm new to collecting steelbooks and just have a few questions as I couldn't find any posts regarding this. What are G1 and G2 steelbooks exactly? Also, when you buy just the steelbook itself, is the game that it originally came with any different than if you were to buy the standard game? Any other information you guys could provide that I may not know or would be good to know is much appreciated.