If you owe back taxes, penalties and/or interest to the IRS and you are not able to pay the entire amount due in one lump sum you might be able to setup an installment agreement.
The IRS will work with you to create an installment agreement that you can stick with in order to pay off your balance, but they do charge a fee. If you owe more than $10,000 setting up an installment agreement you can afford could be difficult.
There are some circumstances where the IRS is required to automatically accept your installment agreement. If you owe less than $10,000 and you can set up monthly payments that will have your tax debt paid in full within three years they will automatically accept your installment agreement. If you owe more than $10,000 or you will need longer than three years to pay off the total amount you owe the IRS can deny your installment agreement.
If you default from the payment plan the IRS can, and often will, demand payment for the full amount still owed.