The words in English can be classified (according to their functions in a sentence) into Parts of Speech.
Noun is simply called as the Naming Word. A name of a Person, Place, Animal, Thing, etc. Examples: Bangalore, Tiger, Table, etc.
There are five different kinds of noun - Proper Noun, Common Noun, Collective Noun, Material Noun and Abstract Noun.
The repetition of a noun in a sentence or a set of sentences is very boring. So, Grammar prescribes that instead of repeating the noun, you may use a word for that noun called as pronoun. So, pronoun is a word used for or in the place of noun. Examples: She, It, They, etc.
A pronoun must itself be something equivalent to a noun. It should not be mentioned until the noun has been mentioned. A pronoun must be of the same number, gender and person as the noun it stands for.
Pronouns can be personal, reflexive, demonstrative, indefinite, distributive, relative and interrogative.
A word that qualifies or describes a noun or a pronoun. Examples:
A verb expresses what the subject of a sentence is or does, or has, or what is done to it.
A word that modifies an adjective or a verb or another adverb. Examples:
Look at the words underlined in these sentences:
The words underlined are called Prepositions because they normally take position before (pre) a noun. The preposition is said to 'govern' the noun that follows it. The noun is said to be the 'object' of the preposition.
Besides single-word prepositions, there are also phrases which do the work of prepositions and are called 'Phrase Prepositions'.
A Conjunction is a word that joins words, phrases and sentences.
Word which expresses a strong or sudden feeling like Surprise, Joy, Fear, Sadness, etc.
It is not grammatically connected with the rest of the sentence. Usually, exclamation mark is put after it.
Examples: Aha! Hurrah! Well! Dear! Oh!