Question [Q] Lenovo A1-07 idea pad android help and questions

Hi there,

I recently purchased an lenovo a1-07 android "gingerbread" and the android platform is rather new to me as I've only owned an ipad. Anyhow it says that it's 16gb but then I see it says 512mb of mddr. When I go into settings I see it has like 12.35gb of internal sd storage and then about 1.49gb internal storage as I have added a few apps. What I don't understand is the storage breakdown and how can I find out the max gb of the sd card that I can use for this tablet. I appreciate any help provided. Thanks in advance for your time.