A budget is a fairly straight forward thing, it a plan and limit on how to spend your money. Basically, depending on your age, the amount of money flowing in your hands would be drastically different, but the concept of a budget stays the same.
Firstly, to plan a budget, one must have a source of money. The source does not have to be steady too, for example, for freelancing workers, the amount of money they earn would fluctuate. Anyway, when you have an idea on how much you have, you have to decide on a goal. The goal would help keep your budget on track.
After the goal is decided, you decide on to time you want to reach the goal. For example, you goal is to buy a house, you google the price of the house and decide how much you want to save. The timing and amount you save is crucial, but more to come later.