Your phone can have two SIM cards which can be used for different purposes.
Select which SIM card to use
Select Menu > > Connectivity > Dual SIM.
To choose which SIM card to use for calls, select Preferred SIM for calls.
To choose which SIM card to use for messages, select Preferred SIM for messages.
To choose which SIM card to use for mobile data, select Mobile data connection > Preferred SIM.
Tip: You can rename your SIM cards to make it easier to distinguish between them. Select Menu > > Connectivity > Dual SIM > SIM settings. Select a SIM card and then SIM name.