Abs are made in the kitchen... So they say. And sure, to some extent this does make sense. Because revealing those abs is only achieved if your diet is in check. But it also implies that you already have a well-built six-pack under that layer of fat. But this is not always the case.
Abs are stubborn muscles, they don't grow easily, and genetics play a very important role in shaping them. Some people have a 4 pack, others a 5 pack, other a 6 or an 8 pack, and this is defined entirely by your genetics. If you were born with a 4 pack, you will never have a 6 pack, no matter how much you train them. You can't make your body grow a nonexistent muscle. But you can push your genetics to give your abs a better and more detailed shape. And to do so you need to eat and train appropriately.
One thing I see very often is people saying that they only train abs when they're cutting (fat loss phase). Which is a mistake, because ironically, it would actually make more sense to train them when you're bulking (gaining phase). Because abs are just like every other muscle, they grow in the presence of a caloric surplus. And while in a surplus your abs may fade away, it doesn't mean they aren't growing. So don't neglect them, you should actually focus on them even more during this period.
My suggestion is training them 2-3 times per week, and with the same intensity as you would any other muscle. And do so year-round whether you're cutting or bulking. Do high reps, low reps, body weight, added weight, and hit them from every angle possible if you want to achieve those 3D abs. And remember, if you want to reveal those abs you've worked for; you need to burn off the layer of fat that's hiding them.
Look at it this way: They grow and achieve a better shape while you’re in a gaining phase (bulking), and you reveal that added mass when you start a fat loss phase. More mass and less body fat = better shaped abs.
And as a last point; abs are aesthetically pleasing but they are also biomechanically important for strength and power. Big strong abs make a stronger core, and a strong core means better lifts. So work on them like you do your biceps, back, legs, etc. Treat them as a primary muscle and not a secondary movement.
Thank you for reading! If you have any questions, leave a comment below!