If Cost Centres have been enabled, the Budgets functionality will include all of the set-up Cost Centres.

When opening the Budgets module, a new column is displayed for the Cost Centre:

Existing budgets will be assigned to the default Cost Centre by default, if they haven’t been assigned to a previously created budget.

When creating a new budget a new field is added to the Budget setup, allowing the selection of a Cost Centre.

This cannot be changed once the budget has been saved, so do ensure that the correct Cost Centre is selected before saving the budget.

Outside of this selection, preparing a budget for a Cost Centre is the same as a normal budget and the process for that can be found here - https://infusion.helpjuice.com/en_AU/budgets/599459-create-a-budget