How to Use the Indefinite Articles A vs. An
The two indefinite articles in English are a and an. The indefinite article an is used to make pronunciation easier when reading a text aloud. The general rule is to use a when the indefinite article precedes a word beginning with a consonant sound and an when it precedes a word starting with a vowel sound.

1 Use a when the indefinite article comes before a word beginning with a consonant sound: a toy a book a house

2 Use an when the indefinite article comes before a word beginning with a vowel sound:an operation an idea an apple

Much / many

Use much if the noun is non-countable (e.g., water, sand). Use many if the noun is countable (e.g., oranges, children). For example:

1. I don’t have much money.
2. They own many houses.

Examples for much / many

1. Phillip owns many properties in France.
2. We didn’t earn much profit this year.
3. How much money have you got?
4. Sharon does not have many friends.
5. There are too many students in this class.
6. It doesn’t need much milk.

Some and Any

The general rule is that any is used for questions and negatives while some is used for positive.

Both may be used with countable and uncountable nouns.

Do we need any rice?

No, we don’t need any rice.

We have some rice in the cupboard.

Some may also be used for questions, typically offers and requests, if we think the answer will be positive.

Would you like some wine?

May I have some more chocolate?

A lot of is used for positive.

There were a lot of people at the party.