Create folder within a folder made by a variable

I’m a powershell nub so bear with me please. I’ve been googling for like the last hour and still haven’t found an solution to my simple problem. I have this section of a larger script that ask the user for a username. It then creates a folder with that variable. What I want to do now is create a folder within that newly created folder. In my googling I ran into a command called “$Using” but it doesn’t seem to be a valid command.

Link to current script

For example Lets say my username variable is “terror”

I want the script to make c:terror

Then I want it to make c:terrorfolder1