The Keybaord section will snap to the case and teh tablet case can be used with out the keyboard attached. THe way the keybaord attaches to teh tablet also helps to hold the two cases together. The keyboard section has elastic straps in the corner to hold the keyboard in. Very good case I think and I am particular about these kind of things.
For SD cards I think. Although they do look a lot like the key holder slot you would find in some wallets and such. You can expand the memory of your Asus with a mini SD card. Those slots would be the right size for the full size sd card adapter.
There is a pen/stylus holder on the side edge of the case.