Hi Praveen,
Request you please look at the below links which give more information about Primary and Secondary cost elements.
Primary and Secondary Cost Elements - ERP Financials - SCN Wiki
primary and secondary cost element | SCN
Primary cost elements are those created from FI G/L Accounts and they do impact the financial accounting of the organization. Example are the Travelling expenses, other cost that are linked to P&L Accounts.
Secondary cost elements are only created in controlling and have no impact on financial accounting of the organization. The use is only for internal reporting only. Examples are internal order, activity type, etc these can be redistributed within the controlling area.
I hope the above makes it clear.
Regards,
Vishal