I used one before in college. Both a and an are used as indefinite articles before the singular of countable nouns to modify countable nouns. What we should pay attention to is that the nouns at the beginning of consonants are preceded by a; An is used before nouns that begin with vowels. The u in the university is pronounced as a semi-vowel /ju/, which is regarded as a consonant. The indefinite article A is used to connect the university. But if it is umbrell, where u is a vowel /a/, the indefinite article an should be used to connect umbrell.

The jingle of one and one usage

The indefinite articles a and an, and the consonant an after a generally refers to one or another. The tone of the table number is weaker than one, and the table before the ordinal number is again. Most has an extraordinary meaning, and abstract matter has become concrete usage. People laugh at the wrong a/an, and single names generally mean being thrown away, referring to everything, which is even more embarrassing.