Tasks vs Expenditure Types definition

Hi,

I am implementing Oracle Projects and I am having issues to arrive to the definition of the projects WBS and expenditure types for the client.

Is it fair to say that while the tasks are the components of the project scope, activities performed to deliver the project or the products resulting of the project delivery the expenditure tasks are the categories of expenses incurred to deliver/perform each one of the tasks within the WBS?

Any advice in terms of the approach that can be used to make the client understand what exactly needs to be taken in consideration to define these structures will be very appreciated.