Pokémon Omega Ruby and Alpha Sapphire/Petalburg City

Petalburg is not large, compared to the metropolises ahead, but it's your first real city, and it contains a few interesting people...

Hi, Dad!
Upon your arrival in Petalburg City, heal your team and fill up on supplies at the Center and Mart respectively. Then go to the north of the city, where the Petalburg Gym lies. Your dad is out the front, having just seen off a challenger. He's thrilled to see you and even more excited to realize that you've become a Pokémon Trainer in your own right. Alas, your dad won't let you challenge him (and for good reason, as his team is around 25 levels higher than yours at this point) until you've obtained four Gym Badges. Never mind, we'll be showing him who really is the best Trainer in the family eventually.

Suddenly a young man appears and asks your dad for help in catching a Pokémon. His name is Wally; he's moving away from home, and he wants to catch a companion to go with him. Your dad thinks this is a great idea and gives him a Zigzagoon, and asks you to supervise Wally. There's nothing you need to do here--the game will automatically move you back and forth. Wally will go into the grass in Route 102 and catch a Ralts. If you know anything about this particular Pokémon's evolution, pay close attention to its gender. Wally is extremely grateful to you and your dad and departs with his new friend. We'll be seeing him again soon.

Your dad suggests you go to Rustboro, a large city to the north of Petalburg Woods, where you can obtain your first Gym Badge. Aside from talking to the locals and picking up some advice on how to play (you can speak to Wally's family, if you like, they're in the house next to the Gym), there's not a whole lot else to do in Petalburg yet, so this is good advice. Make sure your team is in top shape and head to the western exit into the southern part of Route 104.