Coming from Mt. Moon, you’ll arrive in the eastern half of Route 4, which leads directly to Cerulean City. Follow the route east. You can relax as no trainers lie between here and your next destination. First, hop over the ledge directly below and pick up the Paralyze Heal by the corner.
Then make your way east, while keeping towards the north. At the top of the nearby small ramp is 5 Poké Balls with your name on them. Next, continue in the same direction, but keeping towards the south. In the bottom-right corner is a Repel. Finally, go directly north.
You should see an item ball at the end of a ledge, but out of reach. To its left, search the bush to find a hidden PP Up Now head east all the way. At any point that you feel like, jump over the ledges along the south. But note that you cannot go back to Mt. Moon, so if you have unfinished business there, now’s the time to go backwards.
Power Points (PP)
Every move has a certain number of PP, displayed to the right, which indicates how many times you can use that move. As a rule of thumb, the stronger or more useful the move, the less PP it has.
If a move’s PP is running low, you can restore it by visiting a Pokémon Centre or using certain items like Ether or Elixirs. You can also use PP Ups to increase a move’s maximum PP, allowing you to use it more often.
Towards the left, there’s a thick patch of tall grass if you want to go hunting for more Pokémon. Otherwise, keep going east to reach Cerulean City, where you can finally take a breather.
More or less the same Pokémon as Route 3, including Charmander as a rare spawn. However you can also encounter the Water-type Psyduck if you’re lucky. That said, don’t bother searching for Psyduck here, as it will become more common very soon.