1.

I have a brother and two sisters. I love my family. (Correct)

I have brother and two sisters. I love my a family. (Incorrect)
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2.
She has a cheese sandwich, an apple, and some milk for lunch. (Correct)

She has some cheese sandwich, a apple, and a milk for lunch. (Incorrect)
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3.
My house is in London. It has a living-room and two bedrooms. In the morning I study English, and in the afternoon I work in a store. (Correct)

My house is in a London. (Incorrect)

In the morning I study an English, and in the afternoon I work in store. (Incorrect)

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love
cheese
sandwich
apple
milk
lunch
house

in
London
living room
bedroom
morning
afternoon
store

All nouns are countable or uncountable. Countable nouns have the following properties.

- They can be counted, for example 1 apple, 2 apples, ...etc.
- They can be made plural.
- They can take the indefinate article a/an.

Uncountable nouns have the following properties.

- They usually can't be counted, for example 1 money, 2 money, ...etc.
- They usually can't be made plural.
- They usually don't take the indefinate article a/an.

Some is often used for plural nouns. For example:
- I have some apples.
- I have some food.
This is covered later in more detail.

Here are some common countable and uncountable nouns.

apple
tree
person
dog
kilo
liter

time
rice
beef
money
information
help

Countable nouns often refer to individual things, and physical things. For example: a person, a tree, a kilo.

Uncountable nouns often refer to non-individual things, and abstract things. For example rice is not an individual thing, it's seen as group of hundreds of small grains. Love and sadness are abstract, not physical things.

Some nouns can be countable and uncountable, depending on how they are used. For example:

- Countable : A glass of milk. Here glass refers to one container made of glass.
- Uncountable : You can see through glass. Here glass doesn't refer to one thing, it refers to glass as a substance.

- Countable: He has many papers. Here papers refers to some of individual do*****ents.
- Uncountable: Paper is made from wood. Here paper is not an individual thing, but a general substance.

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Whether something is countable or uncountable takes time to learn and can only be achieved through longterm exposure to English. Also, what may seem logical in your own language may seem completely illogical in English! Learning a language involves learning another culture's point of view, and as always, the guidelines above should be used to help your own understanding rather than as hard and fast grammar rules. Good luck!