There are only three articles in English: a, an and the. Small words, but they are used in almost every sentence.
A or an?
Use an before a vowel sound and a before a consonant sound. It depends on the sound, not the spelling.
- an apple, an hour (silent h), an honest person
- a university (starts with a “yoo” sound), a European trip
The
Use the when both speaker and listener know which thing is meant: “I saw a dog and a cat. The dog was friendly.” Also use it for unique things: the sun, the moon.
No article
We usually use no article for general plural or uncountable nouns: “I love music.” “Dogs are loyal.”