how do we create user ?
is there any way to create them withought being existing as OS ( window/unix) user on the database instance box where database server exists
like some clients not on the server wants to connect?
Thanks

DB2 doesn't authenticate users by itself; it refers to the host operating system. As a result, a user must be known to the operating system in order to be authenticated.

It nees os account on the box where instance for database is created or from the client machine where it connects from to the database ?

It depends on DBM Configuration:
db2 => get dbm cfg

.................................................. ...........................................
.................................................. ...........................................
Database manager authentication (AUTHENTICATION) = SERVER
.................................................. ...........................................
.................................................. ...........................................

If it's so, user account must be on server side, but we can set AUTHENTICATION to CLIENT:
db2 => update dbm cfg using authentication CLIENT
db2 => db2stop force
db2 => db2start

And now authetnication will take place at the client machine, and that's why we need to have user account on the client machine