A verb does action or links; and adverbs modify verbs, adverbs, or adjectives.
Verb - Verbs usually perform an action.
Example: Jane walked to school.
^ Here, the verb is "walked," as Jane is doing the walking
Verbs can also be used to connect things.
Example: I am here.
^ The word "am" is a verb. The only easy way to remember which verbs are what type is to memorize them.
Adverbs can modify verbs.
Example: I walked swiftly.
Usually, adverbs end in "ly," but they don't always.
Adverbs can modify adjectives
Example: I walked insanely fast.
^ You know insanely modifies "fast" because you wouldn't say, "Did I walk insanely?" No, you walked "insanely fast."
Adverbs can modify other adverbs.
Example: I almost never walk to school.
^ Here, "almost never" modifies the word "walk," but "almost" modifies "never."
Verbs describe actions. With verbs you can answer questions like: What does he do?/What is he doing?
Adverbs give additional information about action. They can answer questions like: how?/when?/why? and so on.
A simple sentence with a verb only: A baby was crying. About this action you only know it took place.
If you add an adverb you can describe some details of the action. A baby was crying loudly. In this sentence an adverb loudly gives more details describing how the baby cried