Problem with configuring dlink and at&t

Hello, my boyfriend and i bought a laptop from one of our friends and it came with the d-link card and the router. we are able to get on the internet but through an unsecure network. we called at&t to get internet connection so they sent up a modem with the ethernet cord but the ethernet cord is not compatible with the laptop cause no ethernet connection. SO my question is i want to use the d-link card and router but how do i get my own internet service cause at&t is dumb and its not working