A budget is a plan for your money. It helps you track income and expenses. This is a step many people miss or do not feel like doing. In some circles they do not recommend budgeting as they feel it does not work. At the very least you should know what you are spending money on.
Your income, minus your expenses is your profit. You need to know whether every month you have more money coming out than coming in. You cannot pay your debt, start saving, or invest if you are spending more than you bring in.
This is why you need to start by knowing how much income you make every month. You hopefully will have some money going to a 401(k) and savings when you start your budget. This is easily done with your human resources or payroll department.
The next thing you need to do is list everything that is a fixed expense. You should know what you pay every month. Some examples include rent, cellphone bills, and streaming services. List them all out. You should then subtract the money you calculated earlier by this amount. This is where you start.
You next could add some items that vary month to month that you enjoy. Things like going out or going on vacation. Please keep your budget in mind. Some may have more than others. Others may need to make some adjustments and live a little more modestly. It all depends on your financial situation.