Adverbs basically are you're main qord modifiers (usually on adjectives, verbs, or another word type). Adjectives are your normal run of the mill descriptive words. When you need to join something, be it a clause, phrase, or just words, we use conjunctions. Need to really express emotion in your writing, than you need an injection (Pow!) Nouns give thing, places, and people (yes that's mixed around) names. Need to make a phrase? You'll probably need little words called prepositions. Pronouns give us divisertity by allow use to replace common names with other names. Last, but not least, you have the action words in verbs.
Collectively all of the parts of speech work together to flow with grammatical syntax.