The gerund
is a construction that has quite a few purposes. One
of them is - as also in English - the construction of
a part of a sentence.
Llorando
me contó su vida = Crying he
told me his life story.
He
was crying when he told me his life story.
As we can see the gerund in English
is formed by taking the verb and adding the ending ing.
eat => eating
sing => singing
cry => crying
swim => swimming
Unfortunately that doesn't
always work the same way as in English. For more details
please see chapter
8.17.
Los
hombres que trabajan. =
The working men. The men who work.
In the example above you can see
that the part-sentence is a description of a noun (the
men), which means it has an adjectival purpose. In that
kind of cases the gerundio
cannot be used in Spanish. A gerund cannot be changed
according to gender and number therefore they cannot
be used adjectivally.
Have
a look at this comparison
adverbial construction
adjectival construction
Riendo salío
por la puerta.
= Laughing he left through the door.
Saludando la muchedumbre
entró en la sala.
= Greeting the crowd, he entered the room.
El pájaro
que canta encanta mi corazón.
= The singing bird enchanted my heart.
La mujer que rie
está nadando.
= The laughing woman is swimming.
estar
+ gerundio forms the continuous
Now we find something very similar
to the continuous forms. They are formed with the conjugated
form of estar
and the gerundio.
present continuous
estar + gerundio
I am eating
you are singing
he is crying
we are swimming
you are greeting
they are laughing
estoy comiendo
estás cantando
está llorando
estamos nadando
estáis saludando
están riendo
¿Qué
estás haciendo? Estoy trabajando.=
What are you doing? I am working.
See the difference!
¿Qué
buscas? Busco trabajo. =
What do you look for? I look for work.
¿Qué
estas buscando? Estoy buscando mi monedero.
= What are
you looking for? I'm looking for my wallet.
The difference is quite clear -
what is somebody doing at this moment in comparison
to what is he doing in general.
¿Qué
están haciendo los niños?
Están durmiendo. =
What are the kids doing? They sleep.
More details on this issue you'll
find in chapter 8.13.
german-grammar.de
italian-online.de 
french-online.de 
