What's the easiest way to understand what an adverb is?

An adverb is a word that modifies (describes) a verb (he sings loudly), an adjective (very tall), another adverb (ended too quickly), or even a whole sentence (Fortunately, I had brought an umbrella). Adverbs often end in -ly, but some (such as fast) look exactly the same as their adjective counterparts. 

Examples:

Tom Longboat did not run badly.

Tom is very tall.

The race finished too quickly.

Fortunately, Lucy recorded Tom’s win.

It’s easy to identify adverbs in these sentences.

Adverbs and verbs

Adverbs often modify verbs. This means that they describe the way an action is happening.

Phillip sings loudly in the shower.

My cat waits impatiently for his food.

I will seriously consider your suggestion.

The adverbs in each of the sentences above answer the question in what manner? How does Phillip sing? Loudly. How does my cat wait? Impatiently. How will I consider your suggestion? Seriously. Adverbs can answer other types of questions about how an action was performed. They can also tell you when (We arrived early) and where (Turn here).

Adverbs and adjectives

Adverbs can also modify adjectives and other adverbs. Often, the purpose of the adverb is to add a degree of intensity to the adjective.

The woman is quite pretty.

This book is more interesting than the last one.

The weather report is almost always right.

Adverbs and other adverbs

You can use an adverb to describe another adverb. In fact, if you wanted to, you could use several.

Phillip sings rather enormously too loudly.

The problem is that it often produces weak and clunky sentences like the one above, so be careful not to overdo it.

Adverbs and sentences

Some adverbs can modify entire sentences—unsurprisingly, these are called sentence adverbs. Common ones include generally, fortunately, interestingly, and accordingly. Sentence adverbs don’t describe one particular thing in the sentence—instead, they describe a general feeling about all of the information in the sentence.

Fortunately, we got there in time.

Interestingly, no one at the auction seemed interested in bidding on the antique spoon collection.

Degrees of comparison

Like adjectives, adverbs can show degrees of comparison, although it’s slightly less common to use them this way. With certain “flat adverbs” (adverbs that look exactly the same as their adjective counterparts), the comparative and superlative forms look the same as the adjective comparative and superlative forms. It’s usually better to use stronger adverbs (or stronger adjectives and verbs) rather than relying on comparative and superlative adverbs.

An absolute adverb describes something in its own right:

He smiled warmly

Placement of adverbs

Place adverbs as close as possible to the words they are supposed to modify. Putting the adverb in the wrong spot can produce an awkward sentence at best and completely change the meaning at worst. Be especially careful about the word only, which is one of the most often misplaced modifiers. Consider the difference between these two sentences:

Phillip only fed the cat.

Phillip fed only the cat.