The budget screen shows you how much budget remains and makes it easy to review where time and budget was spent. To access it, click the 'Budget' icon in the upper-right corner of your screen. (Note: this will only work if you have permissions to see the budget screen)
You can view spend by week, month, task, or person. You can also click through each time entry to enter that card and see exactly what happened. Budget can be refilled easily with a credit card.