onClick event in navigation drawer

You need to add implements NavigationView.OnNavigationItemSelectedListener

public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener

and add method

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
    // Handle navigation view item clicks here.
    switch (item.getItemId()) {

       case R.id.nav_maths: {
      //do somthing
            break;
        }  
    }
    //close navigation drawer
    mDrawerLayout.closeDrawer(GravityCompat.START);
    return true;
}

method to set Listener

private void setNavigationViewListener() {
    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);
}

call method in onCreate()

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setNavigationViewListener()
}