Harry gose to find spongebob

Uhm... it's okay if you're a first time in the Fanfic world(I was the same when I started back in 6th grade).
But you don't have much detail and your grammar is lacking. Have you ever seen a book written like that that was published? For starters, at least create a new paragraph when someone speaks.
For example:
One day when Harry Potter was out in the ocean at Oak Island in North Carolina going snorkeling he found a pineapple so he thought that it was Spongebob's pineapple.
When Harry looked in the window he didn't see spongebob in his pineapple. So he asked Patrick if he saw Spongebob.
And Partick said, "I don't know where Spongebob is, but, I think he is at the Krusty Krab working."
Harry asked, "Where is the Krusty Krab?"
Partick said that the Krusty Krab was down town.

not


One day when Harry Potter was out in the ocen at Oak Island in North Carolina going snorkaling he found a pineapple so he thought that it was Spongebobs pineapple. When Harry looked in the window he didn't see spongebob in his pineapple. So he asked Patrick if he saw Spongebob and Partick said, "I don't know where Spongebob is but I think he is at the Krusty Krab working." Harry asked, "Where is the Krust Krab," and Partick said tha tthe Krusty Krab was down town.

Also, maybe a bit originality. You may have well written:
"Hi" said Bob
"Hi" said Jo
"Wanna do somethin, Bob?"
"No, Jo."
" 'Kay, Bob."

See, was that fun to read? A little bit of humor would do wonders to your fanfic.

With All Due Respect,
Jazzy-chan

One day when Harry Potter was out in the ocen at Oak Island in North Carolina going snorkaling he found a pineapple so he thought that it was Spongebobs pineapple. When Harry looked in the window he didn't see spongebob in his pineapple. So he asked Patrick if he saw Spongebob and Partick said, "I don't know where Spongebob is but I think he is at the Krusty Krab working." Harry asked, "Where is the Krust Krab," and Partick said tha tthe Krusty Krab was down town.