Student looking for a first credit card

Hey guys, I'm a 20 year old student with absolutely no history of any activity. I don't have any students loans and I have never owned my own credit card before, however I'm an authorized user on my grandparents Discover card.

I'm basically wondering where should I look towards to get my first card because I want to start building credit. I technically don't have a source of income because my job is under the table. From what I have learned on this subreddit my best option sounds like getting a secured credit card from my bank, but I wanted to see if there's any realistic possibility I could get approved for something like the Discover IT Student card.