Hi chrisflynn,
Budget can be keyed in different ways:
1. Project Properties -> Financial Summary -> Financial Plan Summary (Section)
Above option is only editable if there are no cost plans created for that project.
2. Project -> Financial Plans - > Cost Plans
Cost plans are used to create detailed financial plans for a specific period of time of the project, by grouping by financial attributes like cost type, transaction class etc. Cost plans can be revised and can mark latest financial cost plan as plan of record and that cost plan can be used to create a budget plan to reflect the approved budget for the project.
More details on how to create cost plans/benefit plans/budget plans are here: https://docops.ca.com/ca-ppm/15-5-1/en/using/getting-started-with-classic-ca-ppm/financial-management/create-detailed-financial-plans#CreateDetailedFinancialPlans-PrerequisitesforCreatingDetailedFinancialPlans
Regards,
Praneeth