how do U pair iPhone 4 with iMac please? I can get as far as listing the device under system prefs burt I get an error box saying cannot connect to network after a couple of minutes of the mac searching for my phone

I cannot get system preferences to pair my iPhone 4 iOS 7.1.2 with my iMac 10.10.4

It goes as far as identifying the phone, saying it is connected but then an error box appears saying there is no network connection

Sometimes it asks me to confirm the code number that appears but that does not always happen. When it does it ends up again telling me there is no network connection

I have usb cable connection between phone and mac when I am trying to do this

Any help would be very welcome

Thank you

Bob