My best guess is that you don't really have strong abs, you're just so skinny that it looks like it. Not to disappoint you, but unless you do core workouts, it's unlikely you'll naturally have strong abs while the rest of your body is skinny. Still, girls will appreciate apparent abs either way, so I wouldn't worry about it until way later in the future. So the easiest place to start for most people is with your arms, but maybe for you it might be your legs since skinny people tend to be excellent, natural runners. Of course you should try and work on each part of your body a little bit each day (or every other day if you're just starting out), but you should focus on either your legs or arms. If you only do work on part of your body at a time, you'll end up looking kind of weird (for example, I have really strong core muscles, really strong leg muscles, and really weak arm muscles and it's really not ideal). Because you're skinny, food is going to be a huge priority for you. You'll still want to avoid junky foods as best as possible, so you'll want to invest in high-calorie, healthier foods like meat, dairy, and nuts. Don't get too discouraged if you don't see progress right away. It comes slow at first but it develops faster and faster with time. And just because you're skinny and you'll probably never get the biggest body out there isn't a reason to be discouraged. Lots of girls like smaller guys with muscles. That's probably about the best advice I could give you, but keep in mind I speak from experience and I am no means an expert here.