2FA (Two Factor Authentication) is a security mechanism that makes it that when a user logs into such an account, it will flash on another signed-in account, to either allow access or deny that it was you.
In the future, Google hopes that passwords won't be needed at all!
They still haven't said when it's safe to do this extremely risky feature, but they're still discussing whether or not they should.
Though a huge amount of users do already use 2FA, the company asks for people to activate it as soon as possible.
Soon though, the feature will have to be activated, or you cannot create an account.
The company has made a help site here, but if you'd rather not watch it, just do these steps.
This will add an extra security measure for signing in on a device. But to use it, you have to have another device that has Google services pre-installed.
To check if you have 2FA, check here