No one can see your tax return so we can only offer our best guesses without more details from you. The usual reason would be that you did not have enough federal tax withheld from your paychecks. If the amount in box 2 of your W-2 is less than the amount of your tax liability ---- then you owe.
Going forward, you might want to change the W-4 you give to your employer to have more tax withheld.
https://www.irs.gov/individuals/tax-withholding-estimator
https://www.irs.gov/pub/irs-pdf/fw4.pdf
And of course, always check your own data entries, looking for errors such as misplaced decimals or extra zeros.
https://turbotax.intuit.com/tax-tips/tax-payments/video-why-would-i-owe-federal-taxes/L3VXudPiN
If you have federal tax due you can pay by mailing your payment with the 1040V voucher, (which has the address printed on it, having the payment taken out of a designated bank account, or you can pay directly on the IRS website.
https://www.irs.gov/payments
https://ttlc.intuit.com/community/tax-payments/help/how-can-i-pay-my-federal-taxes/00/26212
https://ttlc.intuit.com/community/tax-payments/help/how-do-i-pay-my-irs-tax-due-with-a-check-or-mone...
To apply for a payment plan with the IRS
Apply Online for a Payment Plan
You must pay your state tax due using the state’s preferred method of receiving payment. For most states that will be by making a payment to the state’s own tax website, or by mailing a check or money order.
https://ttlc.intuit.com/questions/1900884-what-are-my-options-for-getting-my-state-refund-or-for-pay...
https://ttlc.intuit.com/questions/1901670-how-do-i-contact-my-state-department-of-revenue
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
