Add a comma by itself (NO)

add a semicolon between two related independent clauses (complete sentences)

Add a period

add a comma + conjunction (and, or, but, so)

I forgot my lunch on the bus yesterday.

My favorite ice cream is mint chip, but I like cookie dough ice cream too.

My sister admonished me to stay out of her room I went in anyway.

An anonymous letter was left on my desk, I wonder who wrote it!

Raul is an astute student, he studies and works hard in every subject.

The bystanders and spectators erupted as the game went into overtime.

The musical performance was downright magical; I can't wait for the encore!

Leslie helped me rake leaves for my neighbor we knocked it out in under an hour.

Because I left my bike outside, it's grimy and covered in muck.

Whenever I go to the mall, I always stop at Annie's Pretzels.

The school paid homage to their retiring teachers at an end-of-year celebration; it was well deserved after their many years of service.

The students hurtled down the hallways because they didn't want to be late for class.

Janine wanted to run a legitimate business, everything needed to be done correctly and legally.

Texting and driving can be lethal; put down your phone to avoid being another casualty on the road.

When I began renovating my kitchen, I underestimated the magnitude of the task. It's more work than I expected!

The course of true love never did run smooth.

My apartment was very stodgy, but I was able to update and improve it.

I did my utmost on the test, now I just need to patiently wait for the results.

Kasen, and Charles are both legitimate artists.

Most of my house plants are deceased because I forgot to water them.

My utmost favorite series is Harry Potter, but The Keeper of the Lost Cities series is also worth reading.

Make sure you bring your device, and a pencil to class.

Theresa has some legitimate concerns about our group project, and I agree with her.

The weather is turning cold on Monday, so I need to run to the store for a new coat.

You can use a comma, and a conjunction to combine sentences.

You should never use just a comma by itself, but you could use a semicolon instead.

Victoria, and Ryan both wrote compound sentences.

You need to use a comma before a conjunction to combine two sentences together, but you don't need a comma before a conjunction if it is just combining two items in a list.