I can understand why you have a question about that. There are several answers to your question and I'll try to give you a short answer here.

Gertie is right for a start. Actions and activities are often used as an "...ing form".

"...ing forms" are everywhere in the English language and gerunds are just one of those forms. Yes, actions like "swimming" and "cooking" and "reading" and "listening" and so on are the kind of gerund Gertie refers to – and I think that is your question.

At the same time, English uses verb forms in many different ways and we often use two or three verbs in a row in a sentence. Here is an example:

Because of the heavy traffic, they try to avoid driving on that freeway on Friday afternoon.

    The verb "try" can be followed by an infinitive form OR a gerund. In this example, the infinitive (to) is better because "avoid" always must be followed by a gerund if you use a verb. Below are some more examples:

I tried calling three times yesterday. OR I tried to call you three times yesterday. 

    Either one is okay and the meaning is a bit different, but not too important for now.

But the verb avoid always has to be followed by an "...ing" form (gerund)

He seems to avoid meeting me.. 

I'm afraid there are not any real good "rules" about gerund or infinitive, but there are patterns and it takes practice to learn which verbs need an infinitive and which one need a gerund, if you use two or more verbs together.

If I understand correctly, you mean when talking about doing a verb? In that case, we use the gerund form.

Running is hard.

Eating all that food made my stomach hurt.

Skydiving takes a lot of courage.

Studying too much gives me a headache.

Is that what you meant?

Hi!!! Yes, Gertie it was a part of it. But it was more like Rod said, when I have many verbs in the same sentence but each one has a different function. Thank you really much Rod!!! And you helped to remember me that some verbs has specific rules for that  but not all.

Roney thank you I had forgotten thoose rules too.

Thank you to all of you!! I`ll study harder =)