How to use a mini sd card in my iPhone 4s?

I got it in my phone and now can't figure out how to access it. I went into the settings and to usage an I can't find it. I'm so confused. I put a 16gig card in my phone and still only have 3 gig left? I don't get it. Does anyone know how to work it? I could use some advice!

IPhone 4S doesn't take any card except the SIM card. If you've inserted a mini-SD card, you might've inserted it in the SIM tray. If there's a card slot on your iPhone 4S, it's a fake one.

IPhones don't use SD cards, so that slot you put it is actually the SIM slot, not an SD card slot.