Colons are used to:
* Introduce a list: "Here are the things you need: a hammer, nails, and wood."
* Introduce an explanation or clarification: "She had one goal in life: to travel the world."
* Introduce a quotation: "The doctor said: 'You need to get more rest.'"
* Separate two closely related independent clauses, where the second clause explains or expands on the first: "He had a plan: he would start his own business."
To separate independent clauses, you can use:
* A semicolon (;): "The storm raged; the house shook."
* A comma and a coordinating conjunction (and, but, or, nor, for, so, yet): "The storm raged, but the house remained standing."
* A period (.): "The storm raged. The house remained standing."