English grammar problem?
I need an explanation about the usage of 'to' word. I was told that after 'to' word, the root word must come afterward. Example : I got to run now. But sometimes, I saw people using like this : We are used to hearing that news. Can you guys tell me how to use this correctly. TQ in advanced 
Comments
It is incorrect that "to" is only used for verb infinitives. It has many uses. "I am going to school". "School" is not a verb.
In this case the expression "to be used to" which means "to be accustomed to" takes a NOUN or a phrase that acts like a NOUN. The word "hearing" is a verb form acting as a noun. It is called a "gerund".
This is going to confuse you, but there is another use of "used" which does take "to + infinitive". That is the form of the past tense which is often translated as imperfect in other languages. "Long ago, we used to live in that city".
The difference is that in "we used to", the word "used" is the verb. In the sentence, "we are used to..." the verb is "are" and "used to" is acting like an adjective. Sorry if that confuses you.
English is one of the most confusing languages, I have heard. I didn't think that before I was told, because I'm a native American-English speaker, but after seeing certain ways words are spelled and especially after seeing your question, I know why.
"To" when followed by a verb is called, along with the verb, an infinitive such as in "to run." Verbs with "ing" following it are called gerunds such as "hearing." All gerunds are verb forms whose part of speech is actually a noun.
A way to break apart the sentence is to substitute "used" for "accustomed" which means about the same thing in your sentence. "to hearing" is the prepositional phrase that modifies the word "used" or "accustomed." Prepositional phrases tell verbs (used and accustomed) how, when, and where. In this case, it tells "how."
I have included a webpage about the phrase "used to" that gives a simpler and quick response, if you're not getting all the above explanations.