"Had" is used:
* To indicate possession or past action: "The book had a red cover." (It possessed a red cover) or "She had eaten lunch." (She completed the action of eating)
"That had" is used:
* In a relative clause to describe something: "The car that had a flat tire was towed away." (The relative clause "that had a flat tire" modifies "car")
Examples:
* Incorrect: "The house which had a big garden was sold."
* Correct: "The house that had a big garden was sold." (The relative clause modifies "house")
* Incorrect: "The student that had studied hard passed the exam."
* Correct: "The student who had studied hard passed the exam." (Use "who" for people)
In Summary:
* "Had" is used on its own to indicate possession or past action.
* "That had" is part of a relative clause used to describe something.
If you're unsure, consider the sentence structure and the meaning you want to convey.