Unfortunately the credit card system doesn't make sense like that. You need to have built up good credit in order for them to provide one for you. I had a lot of trouble getting my first credit card for that reason. However, in most cases, they'll give a credit card to someone who they know is making a fair chunk of money each year, something like 20,000 would suffice.

For you, since you've already got a bad credit score, and also because you are on disability, the likelihood of a bank giving you a credit card is low.

I think the best way to do it though, if you haven't already, is to go into a bank in person and ask to apply for a credit card. For some reason it's much easier that way than it is if you try to apply online.