Use the semicolon correctly

It's not a colon (:).  It's not a comma (,).  It's a semicolon.
I wonder why they didn't call it a semicomma. Probably because it's all of a comma with part of a colon added to it.
We use the semicolon in only two or three ways in English.  First, use the semicolon between two closely related independent clauses in the same sentence.
EXAMPLE: My brother lost his student ID in the cafeteria; he lost his wallet in the library.
You could replace the semicolon with a period in this example.  However to convey that the thoughts are very closely related, the semicolon tells the reader to associate the two thoughts as being related.

We also use a semicolon between two independent clauses in a sentence joined by a coordinating conjunction.
EXAMPLE:  The alumni finished the float at midnight; but they overslept on Saturday and missed the parade
EXAMPLE:  It snowed five inches in Atlanta; unfortunately for the children, it melted as fast as it hit the ground.

We also use a semicolon between groups of related words already separated by commas.
EXAMPLE:   The morning awoke, peeked out from behind the clouds, and slithered across the field and the front lawn; the sunlight fell across the porch, the swing, and the crepe myrtle;