Using capital letters in English might differ from other languages. Here are some guidelines:

The word 'I' is always written with a capital letter. Newspapers often use capital letters for headlines. We also use capital letters in these situations:

The first word in a sentence.
The first word of direct speech.
When starting a quotation.
For titles and ranks – Captain Sparrow
Proper nouns – names, days, months, roads, cities etc.
Adjectives which are nationalities or languages.
For poetry.

The colon can be used to give details of a word or phrase before it:
I have many hobbies: running, dancing and playing the violin.
I’ve got quite a few things to do this weekend: do the shopping, put my winter clothes away and collect my friend from the airport.
The islands have many attractions: wonderful beaches, a vibrant nightlife, good shopping and an interesting history.

The apostrophe is used to show that a letter is 'missing'. This is most common in contractions:
I'm, he's, we'll, don't, can't, won't and o'clock (of the clock) etc.

The apostrophe is used to show possessions. Here are the ways this is used:

Add 's to a singular noun:
The mobile that belongs to Mary - Mary's mobile.
The car that belongs to my neighbour - My neighbour's car.

We use a question mark after a direct question but not after an indirect question. It is a common mistake to put a question mark after an in direct question.

Indirect questions
Here's a direct question:
‘What do you want?’ she asked.
The indirect question is:
She asked me what I wanted.
Most indirect questions are used in reported speech.

Here are the main uses of a comma (,)

Before 'and' or after the name of a person who is being spoken to.
Sarah, where are you going?
Who are you speaking to, Peter?
It seems to me, Mary, that you were right about the forecasts.

Between items in a list.
He bought wine, pasta, a chocolate cake and a lot of other delicacies.

We use a full stop at the end of a sentence. Some people also put full stops after abbreviations.

Defining relative clauses give information about people, things, possessions, places and times. We use relative pronouns with defining relative clauses.

People – who, that
He's a person who is always punctual.
An anchor man is a person that reads the news.

Things – that, which
A calculator is a device that is hardly used anymore.
The mobile is a piece of technology which we can't do without.

A lot of, lots of, much and many are used in relation to count and non-count nouns so it is useful to remember which nouns are ‘count’ (countable) and ‘non-count’ (uncountable) first:

Countable and uncountable nouns

Countable nouns or ‘count’ nouns are those nouns that can be counted:
An apple, two apples etc.

Uncountable nouns or ‘non-count’ nouns are those nouns that cannot be counted: water, bread etc. Uncountable nouns take a singular verb and are not used with a/an.

A few and few are used with plural count-nouns. A little and little are used with non-count nouns.
It is useful to remember which nouns are ‘count’ (countable) and ‘non-count’ (uncountable) first:

Countable and uncountable nouns

Countable nouns or ‘count’ nouns are those nouns that can be counted:
An apple, two apples etc.

Every and each are used with singular (countable) ‘count’ nouns. It is useful to remember which nouns are ‘count’ (countable) and ‘non-count’ (uncountable) first:

Countable and uncountable nouns

Countable nouns or ‘count’ nouns are those nouns that can be counted:
An apple, two apples etc.