As an American taxpayer, IRS brings you quality services to help you meet your tax mandate and understand your tax responsibility. In your quest on how to pay IRS online, you have two fundamental alternatives to choose from.
These two depend on whether you have an account with IRS.
If you have an account, log into your online IRS account and pay your taxes there (irs.gov/account). Having an account helps you see how much you owe the State as taxes. It also helps you to keep track of your tax payment history.
If you want to pay through your account and you do not have one, IRS allows you to register for an account. Be ready with different documents of identity as required in the registration portal.
If you do not have an IRS account and do not wish to create one, you can still pay IRS using Direct Pay (directpay.irs.gov). It is a service enabled by your banking services provider. This alternative applies charges by the payment service provider (your bank) as a facilitation fee.