Find the Micro-SD card slot which is under the right SIM card slot.

Line up the gold pins of the Micro-SD card with the pins of the card slot. If pins in the slot are hidden, then insert the Micro-SD card with the "MicroSD" print up and the pins facing the slot.

Slide the card into the slot until you either hear a clicking noise or until the card does not move anymore. Do not apply too much force; gently slide it in and stop immediately when it does not move anymore.