English is giving me headaches
What's the difference between these sentences? 
I have read that book.
I had read that book.
I read that book.
3 Answers
He leído ese libro.
Había leído ese libro.
Leo ese libro / Leí ese libro (en estos casos la pronunciación de "read" y el contexto te dan saber cuál es la conjugación usada).
- I have read that book. = He leído ese libro = present perfect tense
- I had read that book. = Había leído ese libro = past perfect tense
- I read that book. = Leí ese libro = preterite tense
- I read that book. = Leía ese libro = imperfect tense
So in English only three. In Spanish four. Therefore English is easier. lol.
Your question was about English so:
I have read that book talks of a past action that continues to the present. It may be more apparent in this example: I have read that book all afternoon, now I am putting it down.
I had read that book talks of a action that started and ended in the past. I had finished the book when he asked me to borrow it.
I read that book talks of a past action completed. I read that book last week.