That category is immunity. 1 means that he has a dependent (either a spouse or a child), so the deduction is relatively small. You are 0, which means that no one wants you to support you, so I will deduct you more. But this is only withholding. When filing tax returns at the end of the year, we will calculate how much tax you should pay according to your actual situation. If you deduct more, you will pay it back, so it doesn't matter.