The 2-Factor Authentication (2FA) login option is implemented to make your account more secure. When enabled, you will have to login with a one-time password that wil be sent to your registered email account in addition to your account password in order for you to log in to Onlive. You can turn off this function should you find it a hassle.
To do so, simply click on your profile icon in the top right corner of the Top Bar. This icon should be available to you on any page. Click the profile icon and select 'Edit Profile'.
On the left side of the Account Settings page, you'll see the toggle for 2FA Login. Flip the switch to whichever option you prefer and hit the 'Save' button on the right side of the Page Title Bar to implement the change.