We all know the best av is your finger. If you don't click the link, read the email or open the attachment you're probably safe. But for those times when your finger does something it's not supposed to do there are Anti-Virus programs, both free and paid, that are supposed to stop bad things from happening. This article says the default av that ships with windows is more than sufficient.
https://www.pcworld.com/article/3434097/why-you-can-stop-paying-for-antivirus-software.html
https://www.pcworld.com/article/3434097/why-you-can-stop-paying-for-antivirus-software.html