Summarize the following:
Once you have the tea, you'll want to leave Celadon, exiting the city to the east (which is the right side of the screen). You don't necessarily need to heal your Pokémon at the Celadon City Pokémon Center, though it won't hurt — there are no enemy trainers on Route Seven. Route Seven is very short and safe compared to other routes — all you need to do to reach the Saffron City gate is walk south, then east (down, then right). Hop or walk down the ledge and enter the skinny, sideways facing building. The only way to get into a fight on Route Seven is to walk through the patch of tall grass above the path you need to take. This isn't necessary to get to Saffron City, however. Inside the gatehouse, you'll see a police officer. Originally, this officer would have kept you from entering Saffron City. Now, however, you'll want to approach him and talk to him — he should take the tea and drink it. After this, he will let you through the gate without any harm done. Congratulations! Exit the building to the right and you'll have made it to Saffron City!

Summary:
Head east to Route Seven. Enter the gatehouse to Saffron City. Talk to the police officer.