Adverbs of frequency are adverbs that are used to describe the frequency of the occurrence of an action. The main adverbs of frequency in English grammar are “always”, “usually”, “sometimes”, “often”, “rarely”, “seldom” and “never”.
The point is to know where to use these adverbs in the sentence since depending on whether we have a “to be verb” or not, the adverb can be used in different parts of the sentence.