Semicolons are used to connect two sentences, to avoid a run-on sentence or comma splice.

Wrong (comma splice): Camping is great outdoor activity, it gets you closer to nature.

Right: Camping is a great outdoor activity; it gets you closer to nature.

Wrong (run-on): My brother Trevor enjoys playing sports he's the captain of a local basketball team.

Right: My brother Trevor enjoys playing sports; he's the captain of a local basketball team.

This is the form for using the semi-colon this way:

complete sentence; complete sentence

The ideas in the two independent clauses should be closely related; the second sentence should expand upon the content of the first sentence. You don't need to capitalize the complete sentence following the semicolon.

2. Semi-colons also separate elements of a list, if those elements contain internal commas.

Semicolons replace commas in a list if using commas would make the list more ambiguous.

Wrong: When I cleaned out the refrigerator, I found chocolate cake, half-eaten, a can of tomato paste, which had a blue fungus growing on the top, and some possibly edible meat loaf, which had been left in there by my Uncle Rufus.

Right: When I cleaned out the refrigerator, I found chocolate cake, half-eaten; a can of tomato paste, which had a blue fungus growing on the top; and some possibly edible meat loaf, which had been left in there by my Uncle Rufus.

This is the form for using the semi-colon in a list:

element 1a; element 2, element 2a; element 3, element 3a