You find them all defined here: http://www.usingenglish.com/glossary.html
look up the main categories, like:
what are the deffintions for the 8 parts of speech
A pronoun is a word that substitutes for a noun or a noun phrase.
Verbs refer to an action or a state.
An adjective modifies a noun. It describes the quality, state or action that a noun refers to.
An adverb is a part of speech that normally serves to modify verbs, adjectives, other adverbs, clauses, and sentences. See: http://en.wikipedia.org/wiki/Adverb
A conjunction is a part of speech that connects two words, phrases, or clauses together. See: http://en.wikipedia.org/wiki/Grammatical_conjunction