An adverb is a word that describes or modifies a verb, an adjective, another adverb, a preposition, a conjunction, or even an entire clause.
Essentially, adverbs give more information to the reader. Notice how the adverbs in the following examples add detail or nuance to the sentence.
Types of Adverbs
Adverbs of Time
An adverb of time shows when an event takes place
She finally left school yesterday.
I am sure we will see each other again.
Adverbs of Manner
An adverb of manner shows how an event or action occurs.
He sat at his desk quietly.
Adverbs of Place
An adverb of place shows the location of an action or the direction in which it moves.
I left my bicycle here.
My goal is to keep pushing forward.
Adverbs of Degree
An adverb of degree tells how much or to what extent.
This cereal is too sweet.
I found the book rather boring.
We all know that cigarettes are highly toxic.
Adverbs of Frequency
Adverbs of frequency tell how often an event or action takes place.
I read daily.
I exercise monthly.
Conjunctive Adverbs
Conjunctive adverbs connect and show the relationship between ideas within independent clauses.
Her blood pressure was rising; therefore, the doctor decided to induce her labor.
I’m didn’t sleep last night; however, I still went to work.
The Placement of Adverbs is Important
Adverbs should be placed as close as possible to the word or words they are intended to modify. Notice how meaning is affected by changing the placement of the adverb in the following sentence:
We nearly lost all of our research material.
We lost nearly all of our research material.
The first sentence suggests that the research material was salvaged, but the second sentence says that most of the research material was indeed lost. Here’s another example:
Clearly, Ronald expressed his discontent.
Ronald clearly expressed his discontent.
The first sentence assesses a situation (i.e., it is clear that Ronald expressed himself). The second sentence comments specifically on the way in which Ronald expressed himself.
Adverb Form
Single-word adverbs have two forms: standard and flat. The standard format is the most common and carries the -ly ending. Flat adverbs do not have the -ly ending.
Adding the -ly ending to an adjective is a common way to form a standard adverb. For example, the adjective quiet (as in, the quiet crowd) becomes quietly (as in, the crowd waited quietly).
Standard Adverb Examples
Randomly
Really
Usually
Simply
Absolutely
Flat Adverb Examples
Almost
Always
Across
Quite
Perhaps
Note about the use of hyphens
Two or more words acting as a compound modifier usually require a hyphen:
She bought some much-needed sandals.
Thank goodness I bought a water-proof smartphone.
But when one of the modifiers is an adverb that ends in -ly, a hyphen is not necessary:
He brought a carefully prepared breakfast.
She is a highly regarded speaker.
Additional Resources
http://grammar.ccc.commnet.edu/grammar/adverbs.htm
The Chicago Guide to Grammar, Usage, and Punctuation by Bryan A. Garner.