OK @ajit,
Now really the only thing remaining here is to configure the LDAP connector correctly. This is the part I can help you the less with, as LDAP servers can be configured in thousands ways, and personally I only used openLDAP, rather than Microsoft Active Directory.
Please note that many other customers already successfully managed to do connect ROR to AD. I vividly recommend to search this forum for examples.
The first I came across is this: LDAP Configuration for Active Directory