Как правильно употреблять в языке a и an

Если мы говорим о неизвестном предмете, то неопределенный артикль будет A / An. Артикль A / An произошел от слова One (один). Неопределенный артикль A / An (который произошел от one) ставим только перед исчисляемыми существительными в единственном числе! Артикль A ставится перед словами, которые начинаются с согласных звуков (acat, a house, a yard), а An – перед словами, которые начинаются с гласных звуков (an apple, an hour). 

A cafe called Bogli was located on Eighth Avenue. This room was a modest place for lunch. Two girls worked there. One of them was called Helen, she was a tall, slim and beautiful girl. And the second is Tilda. Suppose she was not very attractive appearance, but both of them were the best friends. Often visitors came to see Helen. After all, she was very pleasant and sociable. Many men dreamed that she would pay attention to them. One man even gave Helen a puppy, and a golden ring. There was no such attention to Tilda, because she herself worked for pleasure. One day a man came to their place. His name was Mr. Siders. He was tall and thin. He understood that Helen would not pay attention to him, so being in a drunken state he hugged Tilda, and even kissed him. Tilda blushed from shock, and this mysterious man left. After this visit, Tilda realized that she could be loved. Suppose she does not have a beautiful appearance, but this kiss gave her strength. When Helen found out about this, she said, "Why did they notice you"

Tilda was waiting for him, but he did not come. One day he came and apologized for this incident. He said that he had gone over a little with alcohol, so he went to this act. And Tilda began to cry, because for her, this kiss was important. This case changed Tilda for the better. After all, if it were not for this mister, then Tilda would not love herself.

1) The U.S. is in North America
2) Washed by three oceans: the Pacific (and the Bering Sea in particular), the Arctic (with the Beaufort Sea), the Atlantic (and the Gulf of Mexico to the south).
3)) Due to the large size of the country, its length, and a wide variety of geographical features in the United States can be found areas with virtually any climatic characteristics. Most of the United States (located south of 40 degrees c. W.) Is situated in the subtropical climate.
5) Population - 320 million