A semicolon (;) is mainly encountered when separating two independent clauses (remember:
An independent clause contains a subject, a verb, and an object.) As a reminder, you can use:

1. Use a semicolon to join two complete and closely related sentences

Each sentence has to be able to stand on its own, and the two sentences should pertain to the same subject or be otherwise related.

My mother has been knitting all her life; I don’t think she’ll ever stop.

I was constantly reminded to stay strong by my sister; her encouragement and love helped me through some tough years.

Taavetti starts a new job today; she is very excited.

I don’t understand the directions; my teacher must explain them to me.

2. Use a semicolon with conjunctive adverbs (transition words) to join independent clauses.

Jo Dee is interested in taking the class; however, it does not fit in her schedule.

My brother seems short compared to his friends; nevertheless, he is the tallest person in our family.

3. Use a semicolon to separate items in a list where at least one item contains a comma.

She had already lived in Independence, Kentucky; Minneapolis, Minnesota; and New York City, New York.

The items in the bakery window looked delicious: soft, buttery croissants; warm, flaky scones; decadent, gorgeous cakes; and delicate, artisanal chocolates.

The art museum contained some beautiful, classically designed furniture; bronze, plaster, and marble statues; and colorful, abstract modern art pieces.

My first meal at college consisted of cold, dry toast; runny, undercooked eggs; and very strong, acidic coffee.

Without semicolons to separate the items in these two examples, you wouldn’t know where each item began and ended due to the commas already used within the items.

4. Use a semicolon to separate coordinate clauses when they are joined by transition words or phrases.

When a sentence contains more than one clause, each of which is considered equally as important as the other, the clauses are called “coordinate clauses.” They are typically joined by a comma + a coordinating conjunction (a FANBOYS word): for, and, nor, but, or, yet, so. When a coordinating conjunction is not used, a semicolon should be:

My sister and I enjoyed the play; afterward, we stopped for an ice cream cone.

or: My sister and I enjoyed the play, and afterward, we stopped for an ice cream cone.

or: My sister and I enjoyed the play. Afterward, we stopped for an ice cream cone.

Tamesha often misplaces her keys; perhaps she should get a key locator.

or: Tamesha often misplaces her keys, so perhaps she should get a key locator.

or: Tamesha often misplaces her keys. Perhaps she should get a key locator.

He woke up; he decided to go back to bed.

or: He woke up, and he decided to go back to bed.

or: He woke up. He decided to go back to bed.

Both parts of each of these sentences are independent and could stand alone, so they are separated by a semicolon, comma with “and,” or a period.

5. Don’t use a semicolon to connect an incomplete phrase or clause to a complete sentence.

It is a common error to place a semicolon between a sentence and a related phrase. If the phrase on either side of the semicolon cannot stand by itself, the two elements need to be joined with a comma, not a semicolon.

Example:

The dancer twirled and twirled; beautiful and breathtaking as he leapt across the stage.

should be: The dancer twirled and twirled, beautiful and breathtaking as he leapt across the stage.

"Beautiful and breathtaking" is not a sentence. Therefore, you can not use a semicolon to join it to "The dancer twirled and twirled."

6. Don’t use a semicolon to connect two dependent clauses.

Example:

My older sister, who is in college; went to the park.

should be: My older sister, who is in college, went to the park.