App crashes when a button is clicked to load a webview

Check here

     @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
        }

        public void login(View v)  {
            webView = (WebView)findViewById(R.id.home);
    }
}

You Are finding view from setContentView(R.layout.activity_main); and there is no any webview in activity_main.xml so it shows you Null Pointer exception. it can not find view from different layout. use your webview in activity_main.xml

If you want different Activities for each then try it

 public class MainActivity extends AppCompatActivity {

     private WebView webView;
     @Override
     protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

     }
    public void login(View v)  {

            startActivity(new Intent(MainActivity.this, YourWebViewActivity.class));
         }

        }

And your activity which has you want to use your webView

public class YourWebViewActivity extends AppCompatActivity {

 private WebView webView;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.your_webview_layout);

            webView = (WebView)findViewById(R.id.home);

  WebSettings webSettings = webView.getSettings();
    webSettings.setJavaScriptEnabled(true);

    webView.loadUrl("https://www.google.com");
    webView.setWebViewClient(new WebViewClient());
 }

and create a new activity for webView

Hope your issue resolved