what if I don't have a connecter between MacBook and iPhone?

If your MacBook has a USB-C port and you have a recent iPhone you should use the cable supplied in the box. Otherwise you can buy it separately. If you prefer to buy the Apple cable, you can find it on the Apple Store (USB-C to Lightning Cable (1 m) - Apple). Otherwise you can buy a third-party Lightning-USB-C cable with the Made For iPhone certification.

If your Mac has a USB-A port you can purchase this cable from the Apple Store Lightning to USB Cable (1 m) or, as already mentioned, an MFi certified cable.

You can find more info here Collegare iPhone e un computer tramite un cavo - Supporto Apple (IT)

Connect your device to your computer using the cable that came with your device or buy a new one.