an adverb is a part of speech and it modifies the verbs, adjectives or other verbs.
ex : you simply don't understand.
it belongs to the part of speech and it describes an action, an occurrence or a state of being.
ex : she sells sea shells on the sea shore.
they belong to the parts of speech and are called as "describing words"
ex : rita has a very pale face
a noun is the name of a person, place, thing or an idea
ex : Mumabai is a highly populated city
it substitutes a noun or a noun phrase.
ex : she has a positive attitude towards her friends.