Parts of speech such as noun, pronoun, verb, adverb, adjectives, preposition, conjunction and interjection are very important in constructing good sentences as well as speaking correct English grammar.
For example, in the sentence below:
I am very happy to be in this forum.
I is a Pronoun
am is an auxiliary verb
Very is an adverb
Happy is a verb
to and in are conjunction
Forum is a noun