Help Understanding Variables with Ansible

I am trying to learn ansible by doing and it has been a fun journey. I am trying to do an automated software install for linux and copying config and .rc files. I found out that the $HOME linux variable works well, but for some odd reason when I try to use $USER it doesn’t work.

I have tried using the shell module and echoing $USER to register user. I must be thinking about this the wrong way and trying to get it to work has been frustrating.

Please give me some insight if you can to help me get over this hurdle.