Grammar is the set of structural rules that govern the composition of sentences, phrases, and words in any given language.
The basic unit of speech and writing is the sentence. A sentence is a series of words (or combination of words) that form a complete thought.
Pronouns are words that take the place of a noun. Pronouns are used instead of a noun. If we didn't have pronouns, we would have to repeat a lot of nouns! So pronouns are used in place of nouns to avoid repetition.
Verbs are important part of a sentence. A Verb is defined as a word that describes an action, occurance or state of being. It helps to make a statement complete. Every sentence must have a verb at its core. Verbs have four qualities (or attributes) - Mood, Voice, Tense and Number. Besides, verbs also have other forms called verbals.
Tenses play an important role in sentence formation. The tense of a verb shows the time of an event or action. The concept of time can be split into the present (What you are currently doing), the past (What you did some time back) and the future (What you will do later).
Adverb is a word that modifies or describes a verb, an adjective or another adverb. It is different from the adjectives in the sense that adjective describes nouns or pronouns.