Storage device not working?

I’ve bought a 2 terabyte storage device and it has 1.8 which I’m fine with, but once I plugged it in and attempted to connect it with instructions on YouTube and I’m not sure if i done it entirely correct but long story short with it plugged in i go to install games and it says “ clear up __ GB “ as for clear more storage for the game as if it doesn’t have 1.3 TB left and I just don’t know what’s really happening here. Please help someone