If your SIM card was not preinstalled, you must install the SIM card before you can use iPhone.

Insert the end of the SIM eject tool into the hole on the SIM tray.
Press firmly and push it straight in until the tray pops out. If you don’t have a SIM eject tool, you can use the end of a paper clip.
Pull out the SIM tray and place the SIM card in the tray.
The angled corner of the SIM ensures that the card fits only the correct way in the tray.
With the tray aligned, carefully replace the SIM tray containing the SIM card in iPhone.