Give your budget a name, a color, and an icon so it's easy to spot at a glance. Choose the currency you want to track it in and set your spending limit — if you're setting up a recurring budget, this limit applies to each period, not the whole series combined.
Pick a start date and how many months each period should run for; the app will work out the exact end date for you automatically. Then choose your scope — which accounts, categories and tags should count toward this budget. You'll need at least one account, and at least one category or tag; use tags when what you want to track cuts across categories, such as a trip, a client or a project. With tags, an expense counts when it carries any of them, and if you pick both categories and tags it must match one of each; picking a whole category group will automatically pull in all of its subcategories for you.
If you'd like this budget to renew itself, switch on Recurring and say how many periods you want it to run for — each period will hold its own separate spending total.