Generally, it's not recommended to use ONLY the webview for login, so unless you have a very specific use case, you should always use SSO.
That said, you can disable SSO by passing in SessionLoginBehavior.SUPPRESS_SSO to a Session.OpenRequest.
First, you need to familiarize yourself with the Facebook SDK for Android. Make sure you go through the Getting Started Guide, and then the Using Facebook Login tutorial.
Following the tutorial, if you're using the LoginButton, then you can just call
LoginButton authButton = (LoginButton) view.findViewById(R.id.authButton);
authButton.setLoginBehavior(SessionLoginBehavior.SUPPRESS_SSO);
in your onCreateView() method.