As stated above, there are essentially 2 types of cards.

First, those with a specific airline. With those ~25k miles will get you to anywhere in the US, ~50k miles will get you to Europe, etc.

Second, there are cards like the CapOne where you earn points with them and they buy you a ticket with any airline.

The big difference is that the airline miles will get you a ticket (subject to availability) regardless of the price of the ticket, e.g., a $200 ticket costs the same number of miles as a $500 ticket. Many of the second type of programs buy you a ticket and charges you miles based on price, i.e., the more expensive ticket costs more miles.

This is, of course, a gross oversimplification because many programs, like UA, offer both types of choices. I suggest considerable research and basing your choice on your specific needs. You might find that a cash rebate card might actually be your best bet until you settle down, start earning more, and most importantly, start spending more. I've found that the real value of credit card programs does not really kick in until one spends considerably more than the average college student is likely to.

By the way, welcome to FT!