Questions on Samsung cover and proper Micro SD memory card for Galaxy S5

I received the Samsung Clear View Black Folio Flip Cover with Window from ATT. It is supposed to replace the back cover of the Galaxy S5. However, the manual mentions a rubber insulation in the back cover which comes with the unit. Thus, if I use the Folio cover from ATT/Samsung, will I still have water proofing or will that now be eliminated?

Also, I received a 32 Gb SanDisk memory card from Amazon. However, there appears to be two memory cards in the case: a larger one measuring 1" by 1.25" and a smaller one measuring 0.38" by 0.63". Which one should I use and why are there two memory cards in the case?

The small one is your microsd card. That one goes in the phone. The big one is just an adapter so you can insert the microsd card into a standard sized sd card reader if you needed to.

Thanks for explaining the battery use. With regard to the Samsung/ATT Flip cover, is it possible that the rubber seal on the back cover should be removed and then inserted into the Flip cover? The Flip cover does have brackets around the periphery which could hold something.