1.
this is about the external sdcard, i.e. sdcard2 that you mount yourself in the slot
The way Sony has organised their installation of the Android system,
you can not write from the tablet to the sdcard from most apps:
the external sdcard2 has different read-write-rights assigned than the internal sdcard1
You can move files between sdcard2 and internal storage (sdcard1) with Sony's File Transfer app.
Also some file manager apps can write new files on it directly, but most apps cannot 'write/change' existing files on sdcard2 (no editing a text file when you parked it overthere...)
Contrary to the post above: this is NOT the case on all android 4.x.x systems, and this was not the case when the tablet was just released before the updates to android 4.x.x
2.
if you talk about installing apps themselves on sdcard2:
that is also impossible and (i believe) this is the case on all Android systems (unless they are heavily modded).
You can install on (or move to) sdcard1, but you may have problems with the icons appearing on your homescreen after reboots then.
