Just to augment Dilip, the IRS has probably already filed your older returns for you and sent you letters hence your question.
You should definitely talk to an accountant (not a major firm since they will get you to file all years even if you don't need to / shouldn't), but there are some things you should know:
- If you were below a certain income threshold (didn't make enough money), you don't have to file. Don't let an accountant file for you if you were below it. You'll incur pointless penalties.
- If you have non-standard income such as self-employment, the IRS may have left out special taxes, so you may not want to file. Just compare their figure for such year where they filed for you to your accountant's and go with the better.
- When the IRS files for you, they take into account only the standard deduction, so they ignore stuff like student loan interest payments.
- You can negotiate a payment plan as long as the time to total payoff is ~3 years without disclosing your financial situation at all as long as the debt is < $50,000 & you've/they've filed all years you were required to file. Bid "high" on the monthly payment, and the person handling account may tell you what the true minimum is.
This is not tax advice. This is: talk to a local accountant that you trust and won't screw you.