Adverbs modify verbs, adjectives, or other adverbs.

Modifying verbs

The machine performed poorly. John revised the paper earlier. Linda sleeps frequently.

Modifying adjectives

The staff are exceptionally competent.

Modifying adverbs

John writes very well. [Very modifies the adverb well, telling to what extent

Type Examples
Adverb of place Move the throttle forward.
Adverb of time Replace the thermostat immediately.
Adverb of degree The nearly completed report was sent on time.