Gerundio is essentially the -ing ending for verbs in English. In Spanish, the endings are -ando for -ar verbs and -iendo for -er/-ir verbs. Although they used similarly to English, there are some key differences. First notice when you would use the gerund.
It is used most commonly in the progressive tenses, and most often with the verb estar.
Estoy comiendo. I am eating.
Tú estás bailando. You are dancing.
Nostros estamos platicando. We are chatting.
You can also use the gerund with the verbs seguir, continuar, and any verbs of motion, like ir or andar.
Ella sigue hablando. She is still talking.
Ellos vienen corriendo a la fiesta. They come running to the party.
Tú andas chismeando. → You go around gossiping.
You can also use the gerund form of a verb as a way to express the idea of by + present particple.
Leyendo vas a estar bien informado. By reading, you will be well informed.
Viajando ellos ven muchas cosas interesantes. By traveling they see many interesting things.
It is not a noun!
The key thing to remember about the gerund is that it is never used as a noun like it is in English.
Me gusta cantando cantar. I like to sing (I like singing).
Jugando Jugar baloncesto es muy divertido. Playing basketball is very fun.
Forming the gerund
If a verb ends in –ar then the new gerund ending will be -ando.
cantar – cantando
hablar – hablando
poner – poniendo
escribir – escribiendo
There are some irregular forms of the gerund as well. For present stem changing verbs that in -ir change the last vowel of the stem from e to i or from o to u.
decir – diciendo
dormir – durmiendo
morir – muriendo
pedir – pidiendo
servir – sirviendo
venir – viniendo
Other irregular verbs are –er and –ir verbs whose stems end in a vowel. With these verbs just add a y to the end of the stem before adding the normal ending.
creer – creyendo
leer – leyendo
caer – cayendo
oír – oyendo
traer – trayendo
Finally, there are two more irregular verbs to be aware of.
ir – yendo
poder – pudiendo
*Note that the verbs ir, estar, and venir are not usually used in their gerund form, but rather just in their simple tense forms.
When using a reflexive verb in the gerund, you will add the pronoun to the end of the participle (gerund form of the verb) and add an accent,
bañarse – bañándose
ponerse – poniéndose
caerse – cayéndose
morirse – muriéndose