Help has my Macbook been hacked ? & if so what now? TIA ( I've been w make for yrs & never had this occur)

I started getting pop up warnings on my Mac whether or not I was on the net.

They've said the following:

Your iCloud is being hacked

Gmail is being hacked

Critical Virus Alert Virus detected ! Activate your ANTIVIRUS

MAC OS: The system is in danger!

Threat detected. Click to delete

! Detected: Trojan_BO8DF831059

Mac scan required