How do I enter budgets for the variance columns?

Management Reports → Budgets. Choose the entity: if its Xero organisation keeps a budget, that one is shown read-only (synced); otherwise you enter a Saral grid of accounts × twelve months, typed or seeded from last year's actuals with an uplift ('Seeding overwrites every cell'). The latest forecast is a second grid copied from the budget and adjusted through the year; variance stays against budget. The pack's budget column reads whichever is in force.