Bad credit and unsecured credit cards aren't usually used together.
If you are a consumer with a bad credit history, you probably already know how hard it is to get an unsecured credit card. Most people like being able to shop with a credit card that has an unsecured credit limit. Even though it's great to be able to apply for and get a credit card without putting money down, you'll quickly see that a person with bad credit is not likely to get an unsecured credit card.
Since you probably won't get an unsecured credit card if you have credit problems, the best thing to do for now is to look into a secured credit card. There are a lot of different types of secured credit cards for people with bad credit, and each one has different options. Make sure to shop around and compare cards so you can find the one that fits your needs best.
Now, there is no hard and fast rule about when you can apply for and be approved for a credit card with an unsecured limit. However, there are some things that will affect what kinds of cards you will be able to get. For example, a big part of whether or not you can get an unsecured credit card is how much you spend and how much you have in credit.
So, it's not impossible for someone with bad credit to get an unsecured credit card, but the easiest way for most people is to get a secured credit card, build up their credit, and then, if they want to, apply for an unsecured credit card.