Functions of an infinitive in English

The infinitive is a verbal form (a non-finite verb form) which

Infinitive is a grammatical term referring to certain verb forms existing

The infinitive has some properties of the verb. The infinitive names

Actions

States

The infinitive can function as an adverbial modifier of purpose or

I have come here (in order) to help you.
To know English well you have

Now he is too tired to give us an account of his trip.
This new method

The infinitive can have a direct object or a prepositional object

Functions

Infinitive with TO

1)modal verbs: must, can(could), may (might), need
2)verbs(make,let,sometimes help)
3)phrases(had better ,would rather,would sooner)

Infinitive without TO

You must do it at once.
Не can speak German. 
Не made me read this book. 
Не made me read this book. 
I would rather not tell them about it. 

Examples

1) Michael Ockenden ,Collins Cobuild English Grammar,Longman,2005.175 p.
2) Impersonal forms of