There are two ways. The first way is this:
Go north from Solaceon to where the Psyducks were. Keep going north, then turn left. Eventually, you'll get there. But to get there, you have to move the Psyducks. To get rid of them, talk to one of the Galctic Grunts in Pastoria city. He'll run away. You have to follow him. Eventually, he will battle you. After, you will meet Cynthia. She will give you a secretpotion for the Psyducks. Go back to the Psyducks and give them the secretpotion. Then they will move. Tip: It is very foggy. I suggest bringing a pokemon thet knows HM Defog.
The other way is this:
Go east from Eterna city until you get to Route 211. Keep going east and you will get to Mt. Coronet. Move boulders and smash rocks. Go to the other side. Exit and you're there. To go this way, you will need HMs Rock Smash and Strength.
Hope this helped!
Use the super rod in Celestic Town.
There are two places to get it. Snowpoint city Celestic town
You can't you can only see it at celestic town where the old lady shows the picture to you
with surf
HM03 Surf can be received at Celestic Town from the elder. She will give it to you after you press A on the pictures inside the ruins.
Celestic Town
Take of the phyduck
Celestic town shrine
Celestic town shrine
celestic town
Celestic Town is the city/town in which you'll get Surf at.
you have go to celestic town and go route 210
Use the super rod in Celestic Town.
Actually there is no gym leader in celestic town. After you beat pastoria gym go to hearthome city.
the old woman in celestic town gives it to you i think
you need to defeat pastoria city's gym leader
He is in the biggest house of Celestic Town.