1. We use a colon (:) to introduce a series of items and we don’t capitalise the first item of the list (unless it a proper noun, which always start with a capital letter)
You will need to bring the following: a map, a compass and a pair of strong walking boots.
These are my favourite things: books, bikes and football.
I saw the following sights in London: Big Ben, The London Eye and Westminster Abbey.
2. We use a colon to introduce a long quotation.
The author of A Bitter Reality, Poulami Dutta, wrote in her final paragraph:
“I heard this story from an elderly friend of mine and came to know that the husband became mad after this incident, and never returned to his home. He would murmur when he was awake and scream in his sleep. So he lived and so he died. I realised that sometimes we make mistakes unknowingly, and don’t get a chance to mend them.”
3. Avoid introducing a list with a colon if it is preceded by a preposition or a verb.