Hi Prashanth,
If a lead is first created in Marketo (via form fillout, list import, manaul creation etc.) then it is up to the Marketo users to create a campaign that determines when this lead is synced to and created in Dynamics. The lead will NOT sync to CRM by itslef. Often people create campaigns based around their sales process that automatically syncs the lead to their CRM system. So for example if a lead reaches a certain score or status or if the lead performs a particular action such as downloads an important whitepaper.
You can also sync leads manaully (see : section "Syncing Leads to Dynamics"in
https://community.marketo.com/MarketoTutorial?id=kA250000000Kzg2)
Once a lead had been synced with CRM then their is a sync relationship between the Marketo record and the CRM record. There is a background sync that manages this relationship in order to keep the lead's data in sync between Marketo and CRM. Normally this background sync occurs every 5 minutes (can be changed on request) and the sync uses the last modified stamp on records to determine whether they need to be updated or not.
At present the Marketo -> Dynamics sync does not include the camapign object.
Objects synced: Accounts, Contacts, Leads, Opportunities* (Read-Only).