Hello and welcome.
I am not a big fan of antivirus apps, or all-in-one third-party utilities such as MacKeeper/CleanMyMac/etc. Much of the time, they cause more harm than good. I do have an external hard drive and a few USB flash drives that I use to perform maintenance on my Macs, which have a whole suite of utilities. I do have
ClamXav, which is not installed on my main Mac, but is only run once a quarter from the diagnostic hard drive. It has never found any viruses, nor have I ever had any on any of my Macs over the years. The only issue I had was a Microsoft Word macro virus back in the '90s. Microsoft actually put out an update that fixed the vulnerability issue.
Historically, Macs have been free of viruses, because they are normally Windows executable files/applications, that simply cannot run on a Mac. Yes, they can downloaded, but they cannot execute/run to cause any damage. You can pass them along to your PC friends however, if they are attached to an email, or embedded in a file that you distribute electronically. In the past few years, there have been some malware issues, which were quickly resolved by apps like
Malwarebytes. The best practice is a regular maintenance schedule, and not visiting questionable websites, or downloading and installing files that are unknown to you.
There are many antivirus apps out there for Macs, but most of them have a live scan or on-access mode that will slow down your Mac, especially Internet browsing. The live scan modes actually scan every file, process, and website as they are opened, run, or visited.
Hope that helps,
C