If by ‘Network share’ you mean the ‘Public’ share, then you need to create new, private shares, which the administrator (you) can give access rights to the various users created on the device.
Refer to chapter 6 of the user manual for ‘managing users’, and chapter 7 for ‘managing shares’.
I would recommend not putting anything in the ‘Public’ share (unless you want it be be public), not even media, since anyone with access to your network will have full access (read/write) to it. Admittedly, you must trust them to some extent, since you have given them your network access password.
Media can be put in any share, and made available via the DLNA media server (see chapter 11, or my Twonky FAQ).
