Once you’ve gone up the stairs into Victory Road, follow the black and white path north. You’ll come upon N who will speak with you for a while before eventually giving you HM05 - Waterfall . You can use this to move up and down waterfalls.
This allows you to explore areas that you wouldn’t have been able to access before, including some that you’ve had to skip in previous places in Unova. All of these areas are listed in the Waterfall Required Areas section. Feel free to check it out if you so wish to.
N will leave soon after. Now follow the path west. Each time you move between two of the pillars, it will check to see if you have the badge that that pillar represents. If you do, it will light up and you’ll be able to continue onto the next pillar.
At this point, you have all eight Gym Badges, so getting through will be no problem. Once you’ve moved through all of them, follow the path north to the main gate. You’ll watch the gate light up, before sliding down into the ground. Once it has, move past it and north to the entrance to Victory Road itself.
Just east of the entrance is somewhat of a makeshift Pokemon Center, outfitted with a Nurse, PC and Poke Mart. Head inside and heal your Pokemon and restock items if you wish to, then head back outside.
First, let’s head east. You’ll see a line of trees moving between two cliffs, move between the trees and the north of the two cliffs. Follow the slightly obscured path all the way along and you’ll find TM01 - Hone Claws at the end. Grab it, then backtrack all the way back to the entrance of the Pokemon Center.
Just south of the ledge to the south-east is a path leading to a few nice items. Move into it and take the south past first. At the end of the path is a hidden Iron. Now head back and take the west path. When you reach the two trees, you’ll see a path leading east on the opposite side, with a rock at the end.
Examine this rock to find a Dusk Stone . Head back to the main path, then continue south, then east. When you see the first path leading south along this path, take it and head to its end. You’ll find a PP Up there. Head back to the path and continue east. Take the second path leading south when you reach it.
Follow this path to the grassy part. When you reach it, head east and then head north up the eastern side of the area. Continue following it north-west until you reach the item just before the ledge. Grab the item, which turns out to be a Star Piece , then jump down the ledge. Head west and enter Victory Road itself.