The job of the colon is simple: to introduce.
1. Use a colon to introduce a list:
- There are three countries in North America: Mexico, the USA and Canada.
- We can see many things in the sky at night: the moon, stars, planets, comets, planes and even satellites.
2. Actually, you can use a colon to introduce a single item, especially when you want to emphasize that item:
- We were all waiting for the hero of the evening: John.
- There is one thing that he will not accept: stupidity.
- The job of the colon is simple: to introduce.
3. Use a colon to introduce direct speech or a quotation:
- He stood up and said loudly: "Ladies and Gentlemen, please be seated."
- John whispered in my ear: "Have you seen Andrea?"
- As Confucius once wrote: "When words lose their meaning, people lose their freedom."
4. Use a colon to introduce an explanation:
- We had to cancel the party: too many people were sick.
- There is no need to rush: the meeting will be starting one hour late.
5. Use a colon to introduce examples, as shown above. For example, item 1 above reads "Use a colon to introduce a list" and ends with a colon followed by two example sentences.