How do I find out if I have any viruses on my computer?

Macs typically do not get computer viruses. However, it may be possible for them to get "infected" by adware or malware.

There are a number of apps out there to attempt to locate and, potentially remove malware. I would suggest that you take a look at either EtreCheck or Malwarebytes for Mac to get started. Again, I would avoid using any anti-virus apps, especially any that "run in the background," as these tend to cause more issues than resolve them ... and we see numerous posts here at the ASC with users asking for help removing them.

The "other side of the coin" is not participating in activities that can get your Mac "infected" in the first place.

Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support

I agree with Tesserax. I sounds as if you have either gotten Mac Cleaner installed or you're seeing adware that is trying to get you to install it.

I'd suggest running Malwarebytes.

Malwarebytes Download - Free Virus Scan & Virus Protection Tool | Malwarebytes

Please note: don't use any links to download it except ones from malwarebytes.com.

See these support articles

macOS Sierra: Protect your Mac from malware

Safely open apps on your Mac - Apple Support

See this article by Klaus1

Viruses, Trojans, Malware - and other aspects of Internet Security

And this one by John Galt

Effective defenses against malware and other threats

Then through some recent threads, Ocarm.

How do I check my MAC for malware?

What is the best way to check my iMac for virus, malware...

I'm so confused about virus and malware on Macs

I think the culprit here is Advanced Mac Cleaner. We get numerous reports here with folks using this app and asking for help on how to remove it. "Cleaner" apps are not required with macOS as the OS has the ability to do its own "housekeeping."

As there are no viruses currently in the wild that affect Macs, that's most likely not your problem. You might want to explain what problems you're having with your Mac. It may turn out they have a different cause.

+1