Use a colon after an independent clause when introducing a list.
The catering facility offers the following entrees: fried catfish, grilled chicken, pan-seared salmon, and sirloin steak.
Use a colon after an independent clause when introducing a quotation.
My teacher’s remark on my final essay was very complimentary: “This essay coherently analyzes musical trends of the late 20th century.”
Use a colon between two independent clauses when you want to emphasize the second clause.
I don’t understand why everyone shops at that store: everything there is so expensive.
https://owl.english.purdue.edu/engagement/2/1/44/
See also:
https://www.quickanddirtytips.com/education/grammar/colons
https://www.grammarbook.com/punctuation/colons.asp
Extra Credit to the first from each class to explain this joke to me:
