You need to answer each point the summons lists...and in similar language in order for it to be filed with the court. You can probably find a summons answer form on one of several legal web sites. You can down load it, or copy it to a word document and fill it in via the computer, then print it out. You will be required to have the answer witnessed when you sign it...by someone who is a notory.
You may not have a choice in the matter however, as your name was also on the card. It really doesnt matter who was responsible for paying it. One question I do have is whether or not you actually signed an application for the card...or did you at any time actually use the card where you would have had to sign your name? If you can say no to both those questions, then you could make the statement that you had not given permission for your name to be added to the card. Then you are not a primary but a secondary user. These companies will come after you in any way they can. They don't care about what is right.
If you did make use of the card, then you must accept the responsibility of paying as you can.

