Go to the Budget page (Menu> Input / Output> Budget) and click on the category to which you want to define a budget, select if you want to set a monthly budget (you will need to enter an amount for each month) or annual (you need to enter a single annual amount which will be divided equally for all 12 months of the year).
Set a monthly budget for all those categories that do not include movements every month, for example, insurance of your car, vacation, etc .. Set an annual budget for all those categories with movements on a monthly basis, as the rent of the house, subscriptions, your salary etc., or for those categories that have a uniform average monthly expenditure.
Note: You can not set a budget for the categories of type "Input / Output".