In the right pane, select Login Approvals and check the Require a security code to access my account from unknows browsers.
To know exactly where your account is logged, access Active Sessions . Here you will see a list of current versions at the top and a list of login times on different devices and computers at the bottom.
If you see any logins that look suspicious (you can know the login location too), click End Activity and change your password.
Good luck!