Route 102 is located at the west of Oldale Town and east of Petalburg City. This is the place where players will encounter their first Trainer battles while walking through Route 102. There is a small pond at north-east of the route.
This will be your first encounter of the Trainer other than your rival. Trainers will not challenge you unless you either speak to them or catch your eye. The Trainers sometimes look around. If you want to avoid a battle, stay out of their sight. It would be better to challenge them so that you will gain experience points for your Pokémon and earn some cash.
There are berry trees all over Hoenn, and the first ones you find are along Route 102. Berries have many uses - it heals HP, cures poison, and can use to create PokéBlocks.
After you pick the berry, the tree disappeared and left the soil alone. You can grow berries by putting one berry on the loamy soil. It will take time to sprout, and if taken care of, it will grow more berries.