Adverbs are words that modify a verb, an adjective or another adverb. Adverbs of manner usually modify a verb; they describe how the action is being performed. Let's look at some examples:

El enfermo estaba comiendo muy despacio.
The sick man was eating very slow.

No solamente come más que tú, también come más rápido que tú.
Not only he eats more than you do; he also eats faster than you.

Tus buenas acciones hablan muy bien de ti.
Your good actions speak well of you.

Some adverbs are formed by adding -mente (-ly)to an adjective:
Adjective ---------------> Adverb

tranquilo (tranquila) - tranquilamente

último (última) - últimamente

ligero (ligera) - ligeramente

Nyscelle está felizmente enamorada.
Nyscelle is happily in love.

Ramón se pierde rápidamente.
Ramón gets lost quickly.

¿Está gravemente herido?
Is he badly injured?

Respire profundamente.
Take a deep breath.

Adela, tristemente ha sido diagnosticada con diabetes.
Sadly, Adela has been diagnosed with diabetes.

Note:

When two or more adverbs ending with -mente occur in a series, the -mente ending is removed from all but the last one. The feminine form of the adjective remains.

Ella habla lenta, clara y deliberadamente.
She speaks slowly, clearly, and deliberately.