make a phone call click on a button

Have you given the permission in the manifest file

 <uses-permission android:name="android.permission.CALL_PHONE"></uses-permission>   

and inside your activity

  Intent callIntent = new Intent(Intent.ACTION_CALL);
    callIntent.setData(Uri.parse("tel:123456789"));
    startActivity(callIntent);

Let me know if you find any issue.