Question [Q] memory various versions?

Hi,

I am shopping for a T-Mobile Note 3 (I am getting rid of AT&T)... mostly shopping online, on craigs list.

I am confused because I have seen several ads from people that say things like "16 Gb Built in" or "32 Gb" or "64 Gb"

I am assuming that this is NOT referring to the SD card, that can easily be swapped out, but to the INTERNAL memory, that CAN NOT be swapped out... My questions:

1) What variations di they make? 16 Gb? 32 Gb? 64Gb? (I thought they only made 32 Gb!!!??)

2) Where on the phone can I find out what it has?

3) If they sold different versions, can the internal memory card be swapped out?

Thank you for any help!

Danny