vs
QUICK ANSWER
"El helado" is a form of "helado", a noun which is often translated as "ice cream". "La galleta" is a form of "galleta", a noun which is often translated as "cookie". Learn more about the difference between "el helado" and "la galleta" below.
el helado(
eh
-
lah
-
doh
)A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
1. (culinary)
a. ice cream 
Comimos helado de chocolate mientras mirábamos la película.We had chocolate ice cream while we watched the movie.
An adjective is a word that describes a noun (e.g., the big dog).
a. frozen 
Una parte del lago Michigan está helado en invierno.Part of Lake Michigan is frozen in winter.
3. (very cold)
c. ice cold 
¡Qué calor! Necesito un vaso de agua helada.It's so hot! I need a glass of ice-cold water.
d. stone cold 
No tomaste la sopa y ahora está helada.You didn't have your soup and now it's stone cold.
5. (astonished)
a. stunned 
Me quedé helada con la noticia del asesinato.I was stunned by the news of the assassination.
la galleta(
gah
-
yeh
-
tah
)A feminine noun is almost always used with feminine articles and adjectives (e.g., la mujer bonita, la luna llena).
1. (culinary)
a. cookie  (sweet) (United States)
Regionalism used in the United States
Agarra una galleta. Acabo de hornearlas.Take a cookie. I just baked them.
b. biscuit  (sweet) (United Kingdom)
Regionalism used in the United Kingdom
Las galletas se están acabando.We're running out of biscuits.
2. (colloquial) (blow) (Caribbean) (Spain)
A word or phrase that is commonly used in conversational speech (e.g., skinny, grandma).
Regionalism used in the Caribbean: Cuba, the Dominican Republic, and Puerto Rico
Regionalism used in Spain