Can anyone tell me please, when in English adverbs are used? what are rules?

Adverbs are used to add information to three other types of words: verbs (think "ADD to the VERB = ADVERB"), adjectives, and other adverbs. The grammar language is that an adverb "modifies" (adds information to) these words.

An adverb modifying a verb:

"I learn foreign languages QUICKLY."

The word "quickly" tells more information about the verb "learn". Here it tells the rate of the learning.

An adverb modifying an adjective:

"I live in a RATHER large house."

The word "large" is an adjective, telling what kind of "house" (noun). The word "rather" adds information to the adjective "large" -- it tells TO WHAT DEGREE it is large.

An adverb modifying another adverb:

"I learn foreign languages RATHER quickly."

Here, the word "quickly" is still an adverb, as explained in the first example above. The word "rather" here tells more about the adverb "quickly" -- it tells HOW quickly.

Do remember that many parts of speech (e.g., noun, adjective, adverb, etc.) may be comprised of SEVERAL WORDS in a "phrase" (without a clear subject and verb within the group of words) or a "clause" (having a clear subject and verb within the group of words).

Ex: "I fell DOWN THE STAIRS."

Here, the subject of the sentence is "I" and the verb is "fell".

The word "down" is a preposition. The word "stairs" is a noun, which is the object of that preposition. (The word "the" is an article, which is a type of adjective.)

However, the entire prepositional PHRASE -- "down the stairs" -- is acting as an adverb, telling WHERE "fell" happened. This is a tricky point of grammar, but it is worth learning -- that adverbs can be words OR phrases OR clauses.