Almost all adverbs that modify other adverbs do so as adverbs of degree, including: very, almost, most, just, least, fairly, incredibly, really, so, and too.
The adverb being modified will be one of time, or manner, and can be "scaled" by these degrees:
Examples:
almost completely
too powerfully,
most beautifully,
so late
least understandably
You can, in some cases, stack them (within reason):
"just so incredibly well"
"almost completely below"
An adverb can modify verbs, adjectives and other adverbs.
It is a verb or a noun, but not an adverb. Adverbs modify verbs, adjectives, and other adverbs.
Adjectives modify nouns. Adverbs modify verbs, adjectives, and other adverbs.
Only adverbs can modify adjectives or other adverbs. They can also modify verbs.
Nouns. Adverbs modify verbs, adjectives, and other adverbs.
Hop is a verb, not an adverb. Adverbs can modify verbs, adjectives, and other adverbs.
Adverbs can modify verbs, e.g. He ran (verb) frantically (adverb). They can also modify adjectives and other adverbs, e.g. That is absolutely (adverb) ridiculous (adjective).
An adverb can modify verbs, adjectives, and other adverbs.
An adverb can modify verbs, adjectives and other adverbs.
Adverbs of degree (so, too, very) can modify other adverbs as well as adjectives. The adverb NOT (adverb of negation) can also modify adverbs (e.g. not fully, not carefully).
Adverbs that modify other adverbs may be either adverbs of manner (e.g. surprisingly well) or of degree (very quickly, too far, exceptionally high, almost always). Adverbs of time or place seldom modify other adverbs.
"Actively" is an adverb. Adverbs modify verbs, adjectives, or other adverbs and often describe how an action is performed.