Regla de "-ing" (Gerundios)

To form a gerund, -ing is added to the simple form of the verb.
Example: talk + ing = talking

Certain spelling rules must be followed to form gerunds:
a. For most verbs, a gerund is formed by adding –ing to the simple form of the verb.
(En la mayoria de los casos, solo agregaremos "-ing")
Examples: walk – walking, read – reading

b.
If the simple form of the verb ends in a single “e,” a gerund is formed by
dropping the “e” and adding –ing. 
(Si el verbo termina con "e", se quitara y se pondra "-ing" en su lugar)
Examples: exercise – exercising, drive – driving

c.
If the simple form of the verb ends in “ie,” a gerund is formed by changing
the “ie” to “y” and adding –ing. 
(Si el verbo termina en "ie", se cambiara por "y" y se agregara "-ing")
Examples: tie – tying, vie – vying

d.
If the simple form of a one-syllable verb ends with a single vowel + consonant, a
gerund is formed by doubling the final consonant and adding –ing. 
(Si el verbo es de una solo silaba y termina en Consonante-Vocal-Consonante, se duplica la ultima consonante y se agrega "-ing")

Examples: shop – shopping, swim – swimming

e.
If the simple form of a verb with 2 or more syllables ends in a single vowel +
consonant, a gerund is formed by doubling the final consonant only if the stress is on the
final syllable.
(Si el verbo tiene 2 silabas o más, termina en Consonante-Vocal-Consonante y la ultima silaba es una silaba tónica, se duplica la ultima consonante y se agrega "-ing")
Examples: commit – committing (stress is on second syllable), combat – combating (stress is on first syllable)

f.
If the simple form of the verb ends in “x,” “w,” or “z,” the final consonant is not
doubled when adding –ing. 
(Cuando el verbo termina en Consonante-Vocal-Consonante y la ultima consonante es "x", "w" o "z", no se duplica y solo se agrega "-ing")
Examples: box – boxing, tow – towing, fly – flying