The word "close" is the opposite of "open." Things that close are doors, windows, containers, stores, accounts, agreements, etc. Pay attention to the pronunciation of this word. The "s" at the end is pronounced as a "z" sound.
In these sentences, the word "close" is used as a verb:
Please close the door.
The store is closing in five minutes.
You need to close this program on your computer before you update it.
They’re going to close their business. (close = end)
The manager brought in a different pitcher to close the game. (close = finish)
We have to figure out how to close this deal. (close = bring negotiations to a successful conclusion)
They’re closing on a house. (They are signing documents for the purchase of a house.)
You can use "close" as a noun:
The sun goes down at the close of day.
The close of the song features a drum solo.
The buzzer on the scoreboard indicates the close of play for a basketball game.
An important part of a young person’s life comes to a close when he or she finishes high school.
Add a "d" to the end of "close" to form an adjective:
That business is closed.
There are several closed factories in that city.
She has a very closed mind when it comes to religion. (closed mind = unable to consider different points of view)