My teacher won't let us start a sentence with articles or pronouns. Are the only articles, "a" "an" and "the"?
Yes. In English there are only 3 articles.
In English there are 3 articles.
A and an are indefinite articles. They are used when introducing an object or a person (only with singular common nouns). A is used when the following word starts with a consonant (a cat, a man). An is used when the following word starts with a vowel (an owl, an eagle)
The is a definite article. It is used to say about object or people mentioned earlier.
I had a sandwich and an apple for breakfast. The sandwich was very good.
In the first sentence each thing is mentioned for the first time, so they have indefinite articles. In the second sentence there is a definite article because the thing (sandwich) was already mentioned.