N5
これ
This
健康。これは大切だ。
Health. This is important.
Explanation
「これ」 means 'this (one)': something close to the speaker. It can stand alone as a subject or object: 「これはペンです」. It cannot go straight before a noun; for that use 「この」: 「このペン」.
Mixed up with
「これ」 can stand on its own in a sentence; 「この」 must always be followed by a noun.
Close to me: 「これ」; close to you: 「それ」; far from both of us: 「あれ」.