After you turn on Two-Step Authentication for your account, signing in will be a little different.
1. You will need your phone.
2. You will log in to your account, as usual.
3. You will then be asked for a One Time Passcode (OTP) from your authenticator app.
4. Enter that code and complete your sign in.
You can disable Two-Step Verification in Your Account.
To disable Two-Step Verification:
When you enable Two-Step Verification you will be provided with an account recovery code.
If you ever lose access to your authenticator app you will need this code to access your account.
It is important that you save your account recovery code somewhere safe when you enable Two-Step Verification. That is the only time you will see this code.