Most languages have eight parts of speech: nouns, pronouns, verbs, adjectives, adverbs, prepositions, conjunctions, and interjections. Each part of speech explains not what the word is, but how the word is used. In order to identify the part of speech of a word, it is necessary to understand the function of the word in a sentence.
Now that you understand the function of each part of speech, you can begin to identify the part of speech of words in a sentence. To do this, ask yourself what function the word is performing in the sentence. Is the word a subject, object, or verb? Does the word describe something? Is the word connecting two ideas? Once you have determined the function of the word, you can identify the part of speech.