To install a Micro SD into your device, first power the device off. Open the tray for the Micro SD card - this is usually the same tray in which the SIM card is installed.
Place the Micro SD card so that it sits evenly in the tray. Replace the tray into the device and power your device on. The device may take a moment to set up the Micro SD card. If you are in doubt, head over to your device's storage settings to check the status of the SD card.