Connect USB cable to PC -> USB logo will show on top of cellphone screen.
Drag that logo down, touch USB Connected/Connection, and touch Mount to PC.
Sometimes, cellphone may require reboot for things to work (Such as in the case where there's an error message saying SD card has been unmounted):
To reboot cellphone, re-seat the battery by sliding the whole back cover of cellphone vertically to remove cover and take out battery. The micro SD card is also retrievable after that.