How to make a fragment open by default in Android? How to sign button which is clicked?

I'm making football application and it has 4 buttons on the top side of the screen. Every button will open different fragment. Now when I open the app by default it's showing 4 buttons and empty field under them where will be shown content of fragments. What should I do so that one of fragments will be opened by default(as MainActivity but it should stay fragment)? Further, how can I sign(note, mark) the choosen button so that user will see which button is selected now? Thanks, if something is unclear tell me and I'll explain further

You can either add a Fragment statically using the activity's layout XML:

<fragment android:name="com.example.myapp.myfragment"
              android:id="@+id/my_fragment"
              android:layout_width="match_parent"
              android:layout_height="match_parent" />

Or you could add it dynamically when your activity starts up:

Fragment myFragment = new MyFragment();       
FragmentTransaction transaction = getFragmentManager().beginTransaction();
transaction.add(R.id.fragment_container, myFragment).commit();