hello! thank you very much. I think I undersand it.

Hola Rocio! So we have many uses for -ing in English. Progressive tense --> 1. An action that is happening right now (ahora mismo) when you are speaking I am eating. = Estoy comiendo. 2. An action that is happening now, but maybe not at the exact moment of speech. He is working in Colombia. = Esta trabajando en Colombia. 3. An action that you are planning to do in the future (a diferencia del espanol!) I am going to the party on Friday. = Voy a la fiesta el viernes. There is also something called the gerund (gerundio), which is like your example with smoking. It is usually the infinitive (infinitivo) in Spanish. Smoking is bad. = Fumar es malo. We can say "To smoke is bad" like in Spanish, but it is not very common and sounds very formal. Lastly, there is the present participle, which may be something like... Boiling water = agua hirviendo It basically acts as an adjective.

When you say "Present Continuous Tense", I'm assuming you mean the "Present Progressive Tense", but to answer your question, in other cases than that the -ing form can be used as a noun to describe an action, as seen in one of the examples you listed: "Smoking is bad for your health." The ACTION of "to smoke" or fumar is changed to the -ing form in order to become a noun that can be described by the adjective "bad".