how to controll second camera (MiniMap)?

For the little square, Make a quad that's on a layer the mini map camera renders(You could parent it to the first camera). And that's no code required.

For the click "Listener", A physics raycast of Camera.ScreenPointToRay(Input.mousePosition) should give a Ray that will give you the location of where the mouse struck, Then its a matter of moving the main camera... Do t$$anonymous$$s w$$anonymous$$le the mouse is over the "PixelRect" of the Camera and w$$anonymous$$le the mouse is actually clicking.

         if (MiniMapCamera.pixelRect.Contains (Input.mousePosition) && Input.GetMouseButtonDown (0)) {
             Ray MouseRay = MiniMapCamera.ScreenPointToRay (Input.mousePosition);
             MainCamera.transform.position = MouseRay.origin;
         }