Usage patterns
〈物〉の部分を直すto fix/repair a part of something
I had the broken part repaired.
〈事〉の部分がわからないnot to understand a certain part (of an explanation, text, etc.)
I don't quite understand this part of the explanation.
〈物〉をいくつかの部分に分けるto divide something into several parts
I wrote the report divided into several parts.
その部分でin that respect/aspect (referring back to a point just mentioned)
I think his opinion is correct in that respect.