MFA means that in order to log into a system, you need to provide more than one piece of information. For example, when you log into internet banking you need to enter a password. That password is a factor. With MFA you need to enter something else. This is why many banks now use one-time codes sent by SMS to verify your identity. That code you receive over SMS is another authentication factor.
A simple way to think about MFA is that logging in requires something you know, such as a password, and something you have like a phone that can receive or generate a unique code. Even if someone knows your password, the risk of them having your phone is very small so they won’t be able to access your account. We see MFA in many other places today. Social media sites use MFA as do many cloud services like Microsoft 365, Google Docs and apps like Salesforce and Xero.