Look at your paper bill the credit card company sends you. Somewhere on the bill will be an internet address. Sometimes it's as obvious as PAY YOUR BILL ONLINE: www. etc. Sometimes you have to search.
Then, it's a matter of going to that website and finding their button for signing up for online transactions. They will ask security questions. Sometimes they will send you an email to confirm. Sometimes you have to actually call someone.
WARNING: Never, ever click on a link you receive in an email from your credit card company asking for security matters. There are a LOT of people who make mock sites that look like they are from your credit card company. You can look up at the URL address and it will not be your creditcard company address. For example, it will say www.adisonfennel.com instead of www.chase.com. When you clicked on the link, it took you to a dummy site. Any information you type in on that site they can take to use your credit card fraudulently. And, any time I receive an email like that, I report it to the fraud section at my credit card.
It's very easy to pay your credit card bill online. Just be wise and careful and read anything they post about security and how to protect yourself.
Hope this helps!