Thank you @Josh Hill for you detailed reply. One quick clarification, if I compare with SFDC, Program in Marketo is a Parent Campaign and Campaign in Marketo is a Sub-Campaign in SFDC?

I am referring to this link in Programs & Campaigns Section - http://developers.marketo.com/documentation/getting-started/
No, not really.
In Marketo: Programs serve several functions
- collect related assets and flows together
- tag Leads as Members and if they Respond or act in certain ways you want them to (Statuses)
- Attribute Opps back to Channels and Offers
- A Program can be synced directly to ONE SFDC Campaign. But it can be any SFDC Campaign and has nothing to do with the SFDC Campaign Hierarchy.
Some people sync the Program to the SFDC Campaign so they are linked, but they aren't necessarily the same at all.
Marketo Smart Campaigns can be inside, or outside, a Program. They are just rules for acting on Leads. They should not be equated to SFDC campaigns.