Let's understand, What is a Clause?

A clause is a phrase with a subject and a verb. In other words, a clause is very similar to a sentence, but a clause is not always a sentence. Is that a little confusing? Let me explain:

A clause contains at least one subject and one verb. These are clauses:
Thomas flew to Paris
even though it was difficult
because she didn't understand
who had come to the party
Jennifer finished the work on time

Only two of these clauses make sense on their own:
Thomas flew to Paris
Jennifer finished the work on time

A clause that can stand alone and make sense is called an independent clause. An independent clause is very similar to a sentence.

Definition:

A main clause expresses a complete idea and could normally stand alone (as an independent clause) if it weren't for the subordinate clause dependent on it. The main clause is in italics in the following examples.

Examples:
I said that I like apples.

The man that I'm talking about lives here.

The other phrases don't make sense on their own:

even though it was difficult
because she didn't understand
who came to the party

In each case, I'm missing information. These clauses are called dependent clauses because they depend on another independent clause to make sense.

Patrick did well on the test even though it was difficult.
She didn't do well on the test because she didn't understand.
He's the man who came to the party.

To sum up, all clauses are either independent or dependent clauses. There are three types of dependent clauses: noun clauses, relative clauses, adverbial clauses.

Noun Clauses

A noun clause is very similar to a noun because a noun clause takes the place of noun in a sentence. For example:
She bought something at the store.
I don't know what she bought at the store.

In this case the noun clause 'what she bought' takes the place of the noun as an object of the verb 'know'.

Noun clauses can take the place of the subject of a sentence.
How she plays the violin is amazing.
What they told us about Tom doesn't make sense.
How she plays the violin = her violin playing
What they told us about Tom = information about Tom

Noun clauses can take the place of a noun as the object of a verb:

Janet didn't understand what Jay said.
Peter didn't buy what he wanted.
what Jay said = object of the verb 'understand'
what he wanted = object of the verb 'buy'

Noun clauses can take the place of a noun as the object of a preposition.

She looks forward to what he says about the deal.
Andrew thought about what she had said to him.
what he says about the deal = object of the preposition 'to'
what she had said to him = object of the preposition 'about'

Noun clauses can also be used a subject compliment to answer the question "What is the (subject of the sentence?)
The toys in the closet are what the children asked for.
Her skills are what they are looking for.
What are the toys? - what the children asked for
What are her skills? - what they are looking for

Adverb Clauses

Adverb clauses are used to explain when, where, why and how something happens. In other words, adverb clauses give additional information to an independent clause it modifies. Adverb clauses are used in complex sentences.

Amlan went to the store because he needed some milk.
If she spent more time on her studies, she would do better on tests.
He'll talk to you when he arrives tomorrow. 
because he needed some milk = the reason why Amlan went to the store
If she spent more time on her studies = stating a condition
when he arrives tomorrow = stating when something will happen

Adverb clauses begin with subordinating conjunctions such as before, if, though, since, while, etc.

Adverb clauses can be placed at the beginning of sentences or at the end of sentences.
My friends went on vacation because they needed to relax.
OR
Because they needed to relax, my friends went on vacation.

Relative or Adjective Clause

Relative clauses modify the noun they follow. Relative clauses con be defining (restrictive). In other words, the relative clause helps define or specify the noun.
I bought the book which Thomas recommended.
She's the girl who telephoned yesterday.
which Thomas recommended = explains which book I bought
who telephoned yesterday = explains who telephoned yesterday

Relative clauses are also used to provide additional information. In this case, a non-defining relative clause is not required, but helps to provide further understanding.
Maggie, who lives in New York, gave a fantastic performance.
Tom Sawyer, which was written in 19th century, takes places in Mississippi. 

who lives in New York = extra information about Maggie - a specific person
which was written in the 19th century = additional information about Tom Sawyer - a specific book

Subordinate Clauses - Concessive, Time, Place and Reason Clauses

Four types of subordinate clauses are discussed in this feature: concessive, time, place and reason. A subordinate clause is a clause that supports ideas stated in the main clause. Subordinate clauses are also dependent on main clauses and would be otherwise incomprehensible without them.
For example:
Because I was leaving.
Concessive Clauses
Concessive clauses are used to concede a given point in an argument. The principle concessive conjunctions introducing a concessive clause are: Though, although, even though, while, and even if. They can be placed at the beginning, internally or at that of the sentence. When placed at the beginning or internally, they serve to concede a certain part of an argument before proceeding to question the validity of the point in a given discussion.
For example:
Even though there are many advantages to working the night shift, people who do so generally feel that the disadvantages greatly outweigh any financial advantages that might be gained.
By placing the concessive clause at the end of the sentence, the speaker is admitting a weakness or problem in that particular argument.
For example:
I tried hard to complete the task, though it seemed impossible.
Time Clauses
Time clauses are used to indicate the time that an event in the main clause takes place. The main time conjunctions are: when, as soon as, before, after, by the time, by. They are placed either at the beginning or the end of a sentence. When placed at the beginning of the sentence, the speaker is generally stressing the importance of the time indicated.
For example:
As soon as you arrive, give me a call.
Most often time clauses are placed at the end of a sentence and indicate the time that the action of the main clause takes place.
For example:
I had difficulties with English grammar when I was a child.
Place Clauses
Place clauses define the location of the object of the main clause. Place conjunctions include where and in which. They are generally placed following a main clause in order to define the location of the object of the main clause.
For example:
I will never forget Seattle where I spent so many wonderful summers.
Reason Clauses
Reason clauses define the reason behind a statement or action given in the main clause. Reason conjunctions include because, as, due to, and the phrase "that the reason why". They can be placed either before or after the main clause. If placed before the main clause, the reason clause usually gives emphasis to that particular reason.
For example:
Because of the tardiness of my response, I was not allowed to enter the institution.
Generally the reason clause follows the main clauses and explains it.
For example:
I studied hard because I wanted to pass the test.
 

Happy reading!!!