A colon introduces an explanation or additional information that illustrates or amplifies what preceded it. What precedes the colon must be a complete sentence.
The company proposes to build two pits: one here and one there.
Colons are also commonly used to introduce a list or a series or even a quote, but again, what precedes the colon must be a complete sentence. (See the Lists section for additional information.)
The document has four goals: one, two, three, and four.
The company said the following: …
Capitalize the first word following a colon only when what follows is a complete sentence, multiple sentences, or a quote. Otherwise, use lowercase.