To pay the IRS:

https://www.irs.gov/payments

Note: Be sure to specify what year and what taxes you are paying. E.g., 2024 1040 or 2025 Estimated Tax.

To Set Up a Payment Plan with the IRS:

https://www.irs.gov/payments/online-payment-agreement-application

To check on your refund:

https://www.irs.gov/refunds

To check on an Amended Return:

https://www.irs.gov/filing/wheres-my-amended-return

Note: At the time this page was published, the IRS is processing e-filed amended returns manually. That is, if the amended return was e-filed, someone is printing those returns on their end, and then the IRS is manually re-entering them into their system in order to process. That is, unlike the original returns, their system is not automated. Thus, amended returns are taking months or even more than a year to process!

To set up an only account with the IRS:

https://www.irs.gov/payments/online-account-for-individuals

You can use an online account to access tax records, make and view payments, view or create payment plans, and view your balance.