infinitive verb and auxiliary verb

Hello!

I am a bit confused!
What is infinitive verb?
What is auxiliary verb?

Just to clarify: the word "to" is not a part of the auxiliary verbs have, need, and ought in the sentences above. These verbs are followed by the infinitive form of the verb:

You HAVE to sing
We NEED to sing
You OUGHT to sing

The infinitive form is also used after the present participle (base verb + ing) in continuous verbs:
I AM GOING to see the fireworks.
We ARE TRYING to fix the car.
etc.

Thanks for ur reply.

I am just using parser software that shows the link between the words of a sentence.

For example, for the sentence " I must go now", the parser shows that

+---I----+
| |
I must go now.

and it explain that I connects certain verbs with infinitives.

In this case , must is infinitive or auxiliary?

I want to speak English perfectly, So what can I do?

The well known split of an infinitive:

to boldly go

Actually, the infinitive of the verb "sing" is "sing," as in "I will sing." (cf. Old Eng. singan; ic willu (want to) singan.)

Forms using the preposition "to" before them are called supines ("I go to sing." cf. Old Eng. ic ga to singenne, where "singenne" is the dative form of a verbal noun used in the same sense as you would say "I go to play or I go to school."

In English, we are so accustomed now to calling the supine form the infinitive, that it's almost becoming correct.