One of the first realities that you will face as a young professional entering the work force is the wall of paperwork associated with starting a new job. And if you are among the majority, you won’t know the first thing about how to fill out these documents, many of which will determine your financial future.

One of the first forms you will see is your W-4, which tells your employer how many federal income taxes to withhold from your paycheck. The Internal Revenue Service recommends filling a new one out each year as your financial situation changes.

The IRS Web site has instructions on filling out the W-4, including a “withholding calculator” that will estimate how exemptions will affect your tax return.

To get started:

• Collect any past pay stubs or tax forms and visit www.irs.gov. Click on the link to “Check Your Withholding.” It will be in the middle section of the Web page.

• Type in all the information they ask, making estimations where you can’t be exact. Just make sure your guesses are based on reality.

• Once you get the calculation, read all the IRS suggestions. They may suggest that you decrease your amount of exemptions or that you must make up X-dollars before the end of the year. This is your ticket to avoiding big surprises come tax time in the spring. Heed their advice.

• If you haven’t started your job yet, you will have made estimations based on your salary and expected taxes. Remember: you can change your withholding amount multiple times in a year; so don’t feel locked in to the exemptions that you write on your W-4.

• Back at your company’s human-resources department, ask how many times you can change your W-4 exemptions.

• Start on the paperwork: write in the exemptions that work best for you (for example, if you are a single 20-something and living alone with no dependents, one or zero exemptions would be typical).

• The more exemptions you make, the fewer dollars will be withheld from your paycheck, so your paycheck will be bigger. But that also could mean you will owe money at tax time (if you do, and you don’t have that money set-aside for such a purpose, the IRS has repayment plans available). On the other side, if you make too few exemptions, you might find that you can’t live on your remaining wages.

• After a few months of working with those exemptions, reassess your financial situation. Are you living comfortably? Use the withholding calculator again and see where you’re at.

On the road to financial security, financial experts say that making smart steps early in life will save you a lot of money and headache in the future. Understanding how taxes affect you as a professional is just one step. Now, get in the habit of saving a portion of your paycheck each month.