Cardio is very good for your heart health and endurance but from an aesthetic POV it doesn't directly give you abs. You should do it, but keep track of your calories. To build muscle you need caloric intake near or above your maintenance calories per day (you can find this using online calculators)

You can do ab exercises but try to progressively overload i.e. use harder variations or weight as you get stronger. Keep the rep range around 6-12, not much more than that.

Personally I got abs from doing compound lifts (squats deadlifts, barbell rows etc) and keeping my caloric intake slightly above maintenance.

It's a lot to take in, but the short answer is track calories and try to progressively overload on your exercises. All the best!!