A clause is a group of words that has a subject-verb combination. A clause may form part of a sentence or it may be a complete sentence in itself. 

Example: He plays basketball regularly.

The above sentence,

→Is a group of words

→Has a Subject- he

A Verb- plays

It satisfies all the conditions. Hence, it is a ‘clause’.

Clauses are mainly divided into two types

1. Independent or main  clause

2. Dependent or subordinate clause

1. Independent or main clause

An independent or main clause is a complete sentence by itself and does not need any other clause for its existence, it makes a sense by itself.

Example:

You may leave.

The above example,

→Is a group of words

→Has subject-you    and     verb-leave

→It has a complete meaning by itself

Hence, it is an independent clause.

2. Dependent or subordinate clause

A dependent or subordinate clause is not a complete sentence by itself. It depends on the main clause to make it a complete sentence. There are 3 types of dependent clauses

1. Noun clause

A noun clause is a dependent clause that acts as a noun. It serves the exact same function as a noun. It can be a subject, object, or complement.

Example:

I am not sure where they went.

I can eat what I want

 

2. Adjective or relative clause

A relative clause is an adjective clause that describes the noun or the pronoun. The clause will start with a relative pronoun e.g. which, who, that, whom, where, or whose. It usually comes directly after the noun it's modifying.

Example:

They caught the thief who stole the crown from the Royal Palace. 

Vegetables that are grown organically are expensive.

 

3. Adverbial clause

An Adverbial clause acts as adverbs. It has a relationship like contrast, condition, reason, etc. with the information that is in the main (independent) clause. With adverbial clauses, the dependent clause can go before or after the independent clause.

Example:

Although he practiced every day, he didn’t win.

She smiled because she knew he was lying. 

Clauses are a very important part of any sentence. A simple sentence usually consists of a single finite clause with a finite verb that is independent. More complex sentences may contain multiple clauses. Practice a few questions to understand this topic better.