Pointing at things: the これ／それ／あれ pronouns and their この／その／あの partners, plus の standing in for an omitted noun.
Stand-alone “thing” words: これ = near me, それ = near you, あれ = away from both.
This is a dictionary.
That (near you) is my umbrella.
これ／それ／あれ are pronouns — they replace the noun and cannot be followed directly by another noun. The choice depends on distance: これ near the speaker, それ near the listener, あれ far from both.
Use this set directly before a noun: この本 = “this book”. Never use これ before a noun.
この ほんは わたしのです。
This book is mine.
あの ひとは ミラーさんです。
That person over there is Mr Miller.
この／その／あの always attach to a following noun. Same distance logic as これ／それ／あれ, but these describe the noun instead of replacing it.
Answer a noun yes/no question with はい、そうです (yes, that's right) or いいえ、そうじゃ ありません (no, it isn't).
Is that a notebook? … Yes, it is.
Is this a ballpoint pen? … No, it isn't.
そう (“so / that way”) + です is a quick way to confirm a yes/no question about what something is, without repeating the whole sentence.
Offer two choices by ending each with か: “Is it A, or is it B?” Answer with the noun, not はい/いいえ.
これは 「きゅう」ですか、「なな」ですか。…「きゅう」です。
Is this a 9 or a 7? … It's a 9.
When the question gives two options, each option takes its own か. You answer by stating the correct option, not with はい or いいえ.
When the noun after の is obvious, drop it: わたしの本 → わたしの (“mine”).
This is mine.
That umbrella is Mr Miller's.
If the modified noun is clear from context, you can leave it out and let の stand for it. わたしの means “my one / mine”.