Ola Nilson! You add '-ing' to the infinitive when you want to use the 'gerund' form of the verb. You can use this when the verb becomes the subject of the sentence: "Speaking helps you learn!" In this example, 'speaking' is the gerund form of the verb 'to speak', and is the subject of this sentence. Also add '-ing' to the verb when it is the complement of a sentence: "My favorite hobby is swimming." In this example 'swimming' is the gerund form of the verb, 'to swim' and complements the subject. Lastly, also add '-ing' when the verb is the object of another verb. "I like learning languages." In this example, 'learning' is the gerund form of the verb 'to learn' and is the direct object of the 'verb 'to like'. The verb 'to like' is conjugated in the present tense, and the verb 'to learn' is turned into the gerund form. I do not speak Portuguese, but this is similar to Spanish, if you're familiar: The verb aprender turns into 'aprendiendo', for instance. I'm not sure what you mean by adding 'to' to the infinitive. The infinitive form of a verb always has a 'to' in front of it: To learn another language is exciting. Here I have used the infinitive form of the verb, 'to learn'. You may notice that the infinitive may be used in exactly the same way as the gerund form of a verb. I hope this helps! Please let me know if I was not clear.

Nilson I'm learned this grammar in this way: If we have a passive verb then can be add " to verb" in continue Look at this: This method is used to solve my problem. And If the subject( who do our sentence's verb) is in our sentence ,again we use " to verb" Look at this: Raymondo use this method to solve my problem. For using of " verb ing" If the subject isn't in our sentence we use this form Look at this: The catalysts for accelerating is found . 90% is seen the " to verb" is used for showing gerund.