I am assuming you have all your records. If they are not complicated and you have done them yourself, simply request the forms (1040, 1040-A, 1040-EZ) from the IRS and complete them. If you are due a refund, don't expect any interest too, since you didn't file to request it until now. If you owe, you WILL be assessed penalties and interest.. A professional could also help you with this if you need it, but be prepared to pay for that service.