The video provides a step-by-step guide to setting up a custom spending plan using the WAB app. It begins by instructing users to open the app, access the menu, and select 'open budget' to start creating categories for expenses. Users can edit default categories, remove unnecessary ones, and add new category groups. Each category can be assigned a custom target amount and frequency, such as weekly or monthly. Users can choose how the target behaves at the start of a new month, either by adding a set amount or refilling only what was spent. For building savings, users can select 'have a balance of' for specific categories. After setting up categories, users can link their bank and credit card accounts to automatically import transactions or manually enter them. The guide emphasizes prioritizing funding for high-priority categories and adjusting allocations as needed. Users are encouraged to record spending to update available totals and reallocate funds from lower priority categories if overspending occurs.