A cost center identifies an area responsible for costs. It is different from a G/L account: the account describes the kind of cost, while the center describes where responsibility belongs. Repairs can therefore use the same account in different centers, and one center can have several expense accounts.
The training client contains CC100 Production, CC200 Sales and CC300 Shared Services. Value help lets you select those keys without guessing from a description. This lesson reads and uses the existing cost-center master data; it doesn't configure controlling areas or validity periods. Check the center on the expense line before you post. A correct account and amount assigned to the wrong center will distort the management report even though the journal still balances.