To insert the cards:
Insert the ejector pin in the hole to partially eject the tray.
Carefully pull the card tray out from the device.
Insert microSD card so that the metal connector faces down with the tabbed side first as shown. Do the same for the nano SIM card.
Things to know about microSD card
You can encrypt the data on your SD card. If you move an encrypted SD card to another device, that device won't be able to see the encrypted data. Decrypt the SD card storage before moving the SD card to another device.
To Encrypt your SD card:
Open Settings > General tab > Fingerprints & security > Encrypt SD card storage.
Encryption takes an hour or more. Start with a charged battery and keep phone plugged in until encryption is complete. If encryption is interrupted, some data will be lost. Tap CONTINUE to proceed.
Follow the prompts to complete the SD card encryption.