“There’s more in the frying pan, sweetums,
Sweetums is a term of endearment.
a loud, hooting noise
Hooting is the noise that owl's make. It can also be used to describe laughter.
Uncle Vernon sat back down
Sat back down means he returned to a seated position
“HOW DARE YOU THREATEN DUDLEY!” roared Uncle Vernon, pounding the table with his fist.
Pouding the table means he hit the table hard with his fist.
Dudley...fell off his chair
Fell off means exactly that. He was on the chair, and then he fell from it.
He roared across the table.
Across means he yelled from his side of the table at Harry, who is seated across the table from him.
I'm sure this book has been translated into many languages. You may want to keep a copy of it in your native language nearby to look at some of these things.
Student or Learner