Your daily calorie budget is labeled 'Kcal Goal'.
'Locked' calories should be burned through physical activity on the present day. They can be unlocked by exercising or using the step counter. Physical activity can also be transferred from the Health app on your iPhone.
'Used' calories include a total of all the calories in the food that has already been logged today.
'Currently available' calories in the chart can be used for food right now, without taking physical activity into account. As you unlock calories, your currently available calories increase, until they reach the Kcal Goal.
The formula behind your dashboard is: Kcal Goal - Locked - Used = currently available.