when I put Windows 10 on a usb and plug it in to my PC what to I use for the activation key?

[snickersniff]

I put the free upgrade onto the usb if that helps.

 

[rgd1101]

for upgrade, it need an activated os on the system you try to do the upgrade.

 

[USAFRet]

The existing OS that you are running it from is the 'key'. There is no activation key you need to enter.
It has to be run from that existing OS.

 

[gangrel]

To UPGRADE, boot normally; plug in your stick; then run setup.exe on the stick. This won't ask for a key; it checks that your current OS is 'approved' and if so, that's your key.

To CLEAN INSTALL, boot from the stick. Now you will need to enter a valid product key, and it's a Win 10 key.