Infinitive

The infinitive is a  base form of a verb with the particle "to" to read, to play, to go.
There are some forms of the Infinitie in English:
                                               Active                            Passive
Simple                                 to write                             to be written
Continuous                          to be writing                     -----------
Perfect                                 to have written                  to have been written
Perfect Continuous              to  have been writing        ------------
Learn more here
 The infinitive can be used with particle to or without it (it is  called the bare infinitive).
Today we'll learn the rules of using the to infinitive.

The to infinitive is used

• to express purpose

I am studying English to travel around the world without problem.

• after certain verbs (agree, appear, decide, expect, hope,learn plan,,promise,refuse,seem, teach,want, etc, )

 She decided to start learning English a month ago.
We want to visit London.

• after certain adjectives which 

- describe feelings/ emotions (sad, happy,glad,sorry,etc.)
She was happy to see him.
-express willingness/ unwillingness (willing, eager,anxious, etc)
He was willing to help us.
- refer to a person's character (clever, stupid, generous, shy,etc)
She was  shy to take part in this discussion.
- and with adjectives lucky and fortunate
I'm lucky to be your friend

• after some nouns and pronouns such as : something, somewhere, anyone, nothing, lot of, etc.

She's got a lot of things to do before her wedding .

• after too/enough

It's too late to go out.

• with it+ be+ adjective / noun

It is interesting to visit the Fine Arts Museum.

• after be+ the first/second etc./next/last/best

She was the first to complete the task.

• after expressions would like , would love, would prefer

I'd like to open my travel agency.

• in the expressions to tell you the truth,to begin with, to be honest, to start with , to sum up, etc.

To begin with,I am a kind and friendly person,