If the your device has a cracked/smashed/damaged screen then you will need a screen replacement.
This repair is to replace the SIM reader. If a device is unable to detect the SIM card, then the chances are the SIM reader is faulty.
Please check the SIM card you are using is registered and on the correct network for the phone.
The Micro USB port is where you plug in the charger. This repair will replace this port so if you are having problems charging your phone or connecting it to your PC then this is the repair for you.