Hi, Tejesh.
>Is the Users created in Gluu UI are also added to LDAP?
Yes, to its internal LDAP db
>What if I have multiple LDAP & want to create under specific LDAP?
You would need to explain what do you mean by "multiple LDAP", but Gluu can have only one internal LDAP server it uses for its own needs, including storage of local user entries. Gluu won't create users in your backend LDAP directories, if that's what you mean.
>Also, how to assign to a Group in LDAP?
There is "Users -> Manage groups" page.
Overall, user management features are very simplistic in Gluu, as it wasn't designed as Identity Management package. They will suite only small scale/test setups. It's expected users are managed through other means and then are simply pushed into Gluu's database.