Explanation:

Adverb:
- In the sentence "I want to go now," the word "now" is functioning as an adverb.
- Adverbs modify verbs, adjectives, or other adverbs. In this case, "now" is modifying the verb "go" by indicating the time at which the action is taking place.
- Adverbs often answer questions like when, where, how, and to what extent. In this sentence, "now" answers the question of when the action is happening.

Function of Adverb:
- Adverbs are used to provide more information about the time, place, manner, or degree of an action.
- They can also modify adjectives and other adverbs in a sentence to provide more detail.
- In this sentence, "now" is specifying the timing of the action, adding clarity to the speaker's desire to leave at this moment.

Placement of Adverbs:
- Adverbs can appear in different parts of a sentence, depending on the type of adverb and the context.
- In this sentence, "now" is placed after the verb "go," which is a common position for adverbs of time.
- Adverbs can also be placed at the beginning or end of a sentence, depending on the emphasis or style of writing.

Conclusion:
In the sentence "I want to go now," the word "now" is functioning as an adverb that provides information about the timing of the action. Adverbs play an important role in adding detail and clarity to sentences by modifying verbs, adjectives, or other adverbs.