SIM cards are for service. You can't access your carrier's/service provider's network without the SIM, that is if they are the type that needs a SIM. Not all do.
Now, if it is in fact a SD card, that is for storage, not service. It is rather odd that there is more than one in the box, if in fact SIM cards. You may want to contact your carrier/service provider and find out why there is more than one.