1. Wrong: His parents gave him everything so he ended up spoiled.
Better: His parents gave him everything, so he ended up spoiled.
Explained: From "His" to "everything" and from "he" to "spoiled" are each complete sentences, so the conjunction "so" needs to be preceded by a comma.
2. Already correct: They helped out when they could and where they could.
Explained: "when they could" and "where they could" comprise a compound predicate, so no comma is needed in this sentence.
3. Wrong: I read the assignment and my teacher gave a quiz on it.
Better: I read the assignment, and my teacher gave a quiz on it.
Explained: Before and after the and are both independent clauses, so a comma is needed with the and.
4. Wrong: Ryan had rejected the offer twice yet Jaime kept asking her.
Better: Ryan had rejected the offer twice, yet Jaime kept asking her.
Explained: The second clause has a new subject and new predicate, so both clauses are independent.
5. Wrong: Richard should study on his own or Pattie can teach him the rules.
Better: Richard should study on his own, or Pattie can teach him the rules.
Explained: The two clauses are both independent in this compound sentence, so a comma is needed.