Your budget should include everything you want or need to spend money on. For example, say your parents gave you $30 to spend while on a school trip to the zoo. However, that does not mean you can spend all your money on a $30 souvenir. The ticket to the zoo costs $10 and you have to pay $5 for your lunch. So, a budget for your trip would look like this.
First, write down how much money you have: $30
Next, write down each item you need to buy: $10 ticket + $5 lunch = $15 remaining
With the remaining money, you can decide if you want to buy a souvenir, some snacks, or save some left over money in your piggy bank when you get home.