An adverb is one of two modifiers in the English language (the other being an adjective) and it can do several things. 1. Modify verbs (ex: he ran quickly), adjectives (ex: he is very tired), or other adverbs (ex: he ran very quickly)
2. In the case of a conjunctive adverb, it can join two independent clauses (ex: he left; however, he came back)