A colon can be used between independent clauses if the second clause summarizes or explains the first.
An independent clause following a colon may begin with an uppercase or a lowercase letter. The Modern Language Association (MLA) and the Chicago Manual of Style recommend lowercase; the American Psychological Association (APA) recommends uppercase. Check with your instructor for the preference in your discipline.
Exercises:
The colon, the semicolon, and the comma 1
The colon, the semicolon, and the comma 2