There are a few short words like 'POCO, MOLTO, TROPPO' that can be used as adverbs or adjectives.
As adverbs they don't change:
Carlo parla poco
Carlo speaks little
Luisa dorme molto
Luisa sleeps a lot
Ho mangiato troppo
I ate too much
As adjectives they do change:
Carlo parla con poche persone
Carlo speaks with a few people
Luisa dorme molte ore
Luisa sleeps many hours
Ho mangiato troppa pizza
I ate too much pizza