これ is often thought to be equal to ‘this’ in English, which is basically correct. これ will always be used to highlight something that is close to the speaker either emotionally, or physically.

• 健康（けんこう）。これは大切（たいせつ）だ。
  Health. This is important. (Emotionally close)
• これも？
  This too? (Physically close)
• これはお菓子（かし）です。
  This is candy. (Physically close)

Despite being translated as a ‘pronoun’ in English, it might be easier to think of これ as a substitute noun (the literal meaning in Japanese), as this is always its function. これ substitutes for something that has its own name, but is not required in the context of the sentence.

• これはステーキです。これはいいです。
  This is a steak. It is good. (これ acts like ‘it’ in English, in the second sentence)