Insert the SIM card, open the mobile phone network, set the network preferences, and set the data flow reminder.
1. Insert SIM card: Insert the mobile phone card into the SIM card slot on the side of the mobile phone, and pay attention to whether the insertion direction is correct.
2. Open the mobile phone network: enter the mobile phone settings, find the "mobile network" option, and open the mobile network.
3. Set network preferences: Go to mobile phone settings and find the "SIM card and mobile network" option. After entering, you can set which SIM card to use by default for Internet access and which SIM card to use by default for voice calls and short messages.
4. Set data traffic reminder: enter mobile phone settings, find the "data usage" option, turn on the "mobile data traffic" option, and set traffic warning and traffic limit.