Have you ever been confused about when to use a colon as opposed to, say, a dash?
When using a colon, think of “as follows.”
A colon can introduce a series of elements or amplify what came before the colon.
Note regarding “as follows”: this applies to run-in lists. If you’re creating a vertical list (maybe using bullets or numbers), the best way to introduce it is with a a complete grammatical statement.
Example: All applications must include the following documents:
A colon can be used between independent clauses (acting a lot like a semicolon), BUT use rarely, and ONLY to show that the second clause illustrates or expands the first.
And occasionally, you can use a colon instead of a period to introduce a series of sentences.
Example: She had several choices: She could…long sentence. She could….second sentence. Or she could…third sentence.
Just keep in mind that generally you want to use a colon to give a sense of “as follows.”
Guidance from Chicago Manual of Style, sixteenth edition (6.59)(6.123)