What punctuation mark is used before a list?
Keep in mind there are some rules about colon usage - and the big one is to know that a list should be a separate but linked thought to the main sentence. So you can say:
These are the things I want: cookies, ice cream, and cake.
I want: cookies, ice cream, and cake (this is better without the colon at all, so I want cookies, ice cream, and cake).