We always begin a sentence with a capital letter. We use capital letters in other parts of the sentence too!
The weather is usually warmer in July and August.
Let's meet at on Alexander Street at 2:00 P.M. tomorrow.
Canada Day is celebrated on July 1st every year.
A capital letter is also used for each part of the name of a person.
The title of a person, such as Ms., Mrs., Mr., or Dr. also begins with a capital letter.
Mrs. Boucher helped us with our science
Alexander Graham Bell invented the telephone.
Dr. Jamie Carver takes care of my grandfather when he is sick.