"How do I know if I'm answering in a correct way?"
I recommend that you send this to fellow entrepreneurs for feedback, before you approach investors. You want to iterate on it, so take your time.
"If I already have a pitch deck?"
No worries, you can use the memo to practise for the questions that investors usually ask in pitch meetings.
"Have you ever written a memo?"
I've done a few angel investments, but I didn't need an approval for a partnership to do the investment. For future investments, I will write memos and share them with you!