used before a noun to talk about one person or thing not mentioned before
I need a pen to write a letter.
used to show someone is part of a group or has a job
He is a doctor at a hospital.
any or every one of something
A cat has a tail and a good sense of balance.
used before a feeling or idea word that has a describing word
She felt a deep sadness after a loss.
used before two things that go together
Please bring a plate and a cup for the party.
used instead of 'one' before some numbers
About a hundred people came to a meeting.
used when talking about how much things cost or how many
Apples cost two dollars a pound at a market.
a person who is like someone else
My brother is a real Einstein when it comes to a puzzle.
used before a name to show you don't know the person
There is a Mr. Smith waiting to see you in a room.
used before a day to talk about one specific day
We always have a meeting on a Monday at a set time.