Hi GVKK,
As sunil mentioned Overheads are usually calculated and planned at percentage Level. Any cost which needs to be booked other than the usual production process into the same Project, demands for an Overhead allocation.
Each of the Transaction is used for Overheads in the project
So feel free o explore them and also make sure you understand the process with the customer
There are lots of information available in the Help Portal
Make good use of it
Regards
Vittal