A conjunction is a word that Joins words, phrases, or sentences .

In simple words:

conjunctions connect ideas.

Common Conjunctions 

and ,but or ,so, because ,although ,if when

Types of Conjunctions (school level)

1 Coordinating Conjunctions

They join equal words or sentences.

Common words:

and, but, or,so

Examples:

. I like tea and coffees

.she is poor but honest.

.Do you want tea or coffee?

.It was ranning so we stayed at home.

2 Subordinating conjunctions

They join a main clause with a dependent clause.

Common words:

because,although, If, when,while, after,before

Examples: 

. I was late because I missed the bus.

.Although he is rich he is kind.

.If you work hard, you will succeed.

.call me when you reach home.

3 .Correlative conjunctions

They work in pairs.

Common pairs.

.either -or 

.neither-nor 

.both -and

.not only -but also

Example:

.Either you or I am wrong.

.Neither Ram nor Shyam was present 

.She is both smart and hardworking .

.He is not only intelligent but also polite.