it means you don't have a license, as your friend built your PC he set you up to have to buy the most expensive licence for ultimate.
He was talking about some windows activator, what is that thing? plz help me what to do?
It's illegal/piracy and we not assist with piracy.
If you don't have a license you'll need to buy one. If you can't afford one install windows 10 and run it unactivated. It will have no personalization features, a watermark and will occasionally nag to be activated but other than that it will function normally and update.