Eterna city

...You need to get to Eterna City, but not THAT way.
First, find the gym leader in the Mines, which is south of Oreburgh City. Then, obtain the first badge. You already have HM06 Rock Smash, since you obtain it by default, so you're all set! Now, go back to Jubilife City, and go north. Go in the cave, go up, then go right and exit the cave, using Rock Smash on those boulders. Then, just go north and into Floaroma Town.

There isn't much you can do at the moment, so heal up and stock up on items, if necessary. Go east onto that route, talk to the little girl, and continue east into the Valley Windworks. Battle the grunt in front of the building, and then go back to Floaroma Town. Go in the northwest corner and into the little forest. Battle the two grunts, and obtain the Key. Then, go BACK to the Valley Windworks, and in the building. Battle all the trainers in this area, and then the commander. Once you're done there, exit, and you can now continue go north of Route 205. Go in Eterna Forest, and help the girl get to the end. Once you exit onto the northern part of Route 205, continue east into Eterna City.

Now that you've reached Eterna City, you want a bike. So, beat the second gym leader, and go north of Eterna City and talk to Cynthia to obtain HM01 Cut. Teach Cut to a Pokemon, and go in the creepy building just to your north a bit more. Beat all the grunts in that building, and then another commander at the end. Exit, and go in the building south of the Pokemon Center, and talk to the guy to obtain a Bike.

With the Bike, just go south and onto Cycling Road, and if you continue south, you'll be on Route 206, and in the area you originally couldn't reach.