The Reti Opening is starting out with the knight instead of a pawn.
This is my favourite opening because it has a lot of shock to it to the defense.
It is quite common but is very good.
Unlike Queen or King pawn opeing you already have a devolped knight.
The best defense against it is the Slav.
The Slav is where you from a triangle of pawns.
The Slav is bassically where if you take you get taken back.
It is super strong when some one has a major attack plan.
Here is a video of how to use the Slav.
Now Obviously this would not happen but shows when white hangs their pieces and tries to attack they get attacked by the king and queen dance.
When using the Reti Opening the point is to develop a piece early on.
It is widely regarded for being the third best chess opening.
So when using it is key to open your kings pawn next allowing a bishop and queen to be developed.
Black had several missed wins but chokes in the end of playing defense.