In English, a gerund is a verb ending in –ing that is used as a noun. It is not just any word that ends in –ing. In the sentence “we are going to the store,” the word “going” is not a gerund. Words that end in –ing and are used with “to be” verbs are present participles, and the result is a progressive tense that expresses something that is ongoing.
In English, both gerunds and infinitives can be used as verbal nouns. The –ing form can appear as the subject of the sentence:
Running is good for you.
Dreaming about your lover is time well spent.
To read is educational.
To work is the best therapy.
Running and dreaming are both gerunds—verb forms used as the subjects of the above sentences. To read and to work are infinitives used as nouns.
A gerund can also be used as an object, either of the verb or of a preposition:
She plans on traveling to Europe.
He thinks about expanding his business.
She loves cooking.
In contrast, the Spanish gerundio (-ndo form) cannot be used as a noun, although texts and grammarians refer to the –ndo verb form as a gerundio. One cannot say “corriendo es bueno” or “soñando te asusta.” Some examples in English and Spanish follow:
Walking is fun.
Caminar es divertido.
Smoking is dangerous.
Fumar es peligroso.
Running is good.
Correr es bueno.
Dreaming scares you.
Soñar te asusta.
In English, the –ing form can be used as an adjective, such as “an interesting life” or “a daunting task.” Again, in contrast, the Spanish –ndo form (gerundio) never appears as an adjective:
She has an interesting life.
Ella tiene una vida interesante.
He has a tiring job.
Su trabajo cansa mucho.
It’s a moving vehicle.
Es un vehículo móvil.
So the Spanish gerundio is essentially equivalent to the English present participle, and its use is similar in that it is used to form the progressive tenses:
She is leaving now.
Ella está saliendo ahora.
He was playing yesterday.
Él estaba jugando ayer.
We had been traveling a lot.
Habíamos estado viajando mucho.
In a sense, the Spanish is simpler, because the use of the gerundio is narrower than that of the English gerund. But taken another way, the Spanish is more complicated, because in verbal-noun and adjectival situations, you have to use different words and different constructions.