There is the main "Public" folder structure - all files within which are visible to everyone. Then there are users that you set up, each has its own folder in the same parent as Public, called User_1, User_2 etc. Files in these are only available to the selected user at the time (at the bottom of the orbiter), and these generally need a PIN entered to access them.
However, you should be aware that there are a few bugs in the current 0710 build. First, in Filename sort mode, you only see Public media not users' media. Second, when you use the search function, you still see all the media irrespective of whose folder it is in and which user you are logged in as at the time. These can make the use of the function a little difficult (or pointless if you are either using it for security or if you haven't tagged all your media).
I know at one point someone said they had fixed those bugs, but it was a while ago and I don't know whether they are still apparent in the 0810 Alphas (consequently I cannot log tickets for them) perhaps someone else can comment on that point?