The adverb "usually" modifies the word "meets" in the sentence "The film club usually meets at the same location". An adverb is a word that adds to the verb. In our case, the verb is the word "meets" so the adverb is "usually". An adverb not only adds to the verb, it modifies a verb, adjective, another adverb etc. Adverbs express place, time, frequency etc. They answer the questions how, in what way, when, where, and to what extent.
