No Lic. Or Purch Request From MS After Installing W10 ?

Hello,

New iMac desktop user, Sr. Citizen, and not too sharp with this "stuff,"
so please bear with me a bit.
Purchased Parallels along with the iMac at Apple store.

a. Used Parallels to install W10 on a separate partition, which I think was successful.
The W10 Desktop that appears now looks like it should, i think, but have not played with it yet.
Question: At no time during the Parallels install did it ask me for a Windows Lic., or
ask for my Credit Card. Yet Windows does appear now after the installation.
Can't believe Windows is free. Did I miss something ?
Why no Lic. Key/Purchase request ?
*Should I use it anyway (don't want to mess anything up), or is there some screen to go to
now from Parallels that will enable me to buy W10 ? If so, where, and how do I go about this ?

b.Should I have used Boot Camp for the W10 install, and Parallels just for the Apple-Windows10 switching ?

c. And, what is the simplest way of going from one to the other; what do I click on if in the Apple side,
and what if I am in the Windows side ? Would like to avoid any and all Password requests and requirements
when doing so.

Thank you very much for help; really appreciate it.

Bob