Hello @Ashish Gupta,
One would subscribe to a service, and in the initial Refresh message for that service, there will be its DACS lock.
To provide additional clarity, the DACS locks are used by OpenDACS API, but not obtained for any service from DACS via OpenDACS.
I would suggest the brief article Introduction to the DACS Entitlement System for OpenDACS Developers , especially section Content Based Entitlements, to better understand how this works.
If you would like a more in-depth understanding of the lock types, creation, and working woth them, DACS Locks Developer Guide in RFA deck may be a useful read.
Hope this was of help