Head west out of Aspertia City onto Route 19. Here, you'll immediately encounter Hugh. He'll challenge you to your very first Pokémon battle! This battle serves as a tutorial for the combat system. Hugh will use the starter Pokémon that has a type disadvantage against yours. For example, if you chose Snivy (Grass), he'll have Tepig (Fire). Focus on using your starter's attacking moves to defeat his Pokémon. Don't worry too much about strategy at this point; it's designed to be straightforward.
After the battle, Hugh will heal your Pokémon and then head off. Continue exploring Route 19. This route is short and serves as an introduction to wild Pokémon encounters. You can find Patrat and Purrloin here. Engage in a few battles to gain experience for your starter. Bianca will eventually catch up to you and teach you how to catch Pokémon, giving you 5 Poké Balls. Use these to catch your first wild Pokémon! Having a second Pokémon can be very helpful for early game battles. Once you've explored Route 19, head north into Floccesy Town.