Rashmi,
epesi is used as a collaborative software and the purpose is to exchange data with other members of your team/organization. The information stored there should be available to everyone - in this case the record will be public - this is default permission. However there may be instances where you would like to store information - accessible by others but you would like to prevent them from modifying it - in this case you wil use protected option. And finally private means that nobody can view it (and of course modify it).
You can also think of it as files attributes:
[list:2lak0mev]
[*:2lak0mev]read/write = public[/*:m:2lak0mev]
[*:2lak0mev]read only = protected[/*:m:2lak0mev]
[*:2lak0mev]hidden = private[/*:m:2lak0mev][/list:u:2lak0mev]
with the difference that hidden means hidden from all users but the creator/owner.
