Question about G3 networks (CDMA, LTE, etc.) topic

So I know this phone has CDMA, LTE, and GSM. My question is, does GSM even work on sprint? I thought GSM was only on At&t and verizon? I thought sprint was only CDMA and LTE?

I am confused about the GSM network. Does it mean that GSM isn't used with sprint but can be since there is a sim card?
I am only on sprint so will i ever need to worry about GSM?