If your credit score is under 600 then it can be hard to get any regular credit cards that most other people get approved for with a good credit score.
When you have bad credit and cannot get approved for a traditional credit card then you can easily get approved for a secured credit card such as through capital one credit card company.
You sign up and apply for the capital one secured credit card and then when you're approved you put up a deposit of around $100.00 to $200.00 which then becomes your credit limit.
You use the secured credit card as you would a normal credit card and then pay the bills on time and when you continue to use the secured credit card like you're supposed to and keep the credit card payments made each month then your credit score will eventually increase.
When your credit score increases after a year or two years then you can apply for and get approved for a regular capital one credit card or any other credit cards.
Having bad credit can make it hard to get approved for normal credit cards but you can get approved for a secured credit card when you have bad credit.