Be sure that you have removed all parts of any previous case. For a slim case - Slide the side of the phone with the most buttons into the case first. Then snap the other side in by pressing the case and phone together.For a tough case - Separate the liner and outer shell of your new tough case. Slip your phone into the TPU liner first. Slide the side of the phone and liner with the most buttons into the case first. Then snap the other side in by pressing the outer shell and phone together.