Adverbs provide more information about verbs or adjectives by describing how an action is performed, how often it is done, how intense a quality is, etc.:

Habla bien. No estudiamos demasiado. Es bastante difícil.

She speaks well. We do not study too much. It is quite difficult.

• Adverbs have no feminine or plural forms, and are placed as close to the verb as possible:

Son bastante difíciles. Las peras están demasiado viejas. Me gustan mucho las fiestas.

They’re quite difficult. The pears are too old. I like parties a lot.

 Some adverbs, however, are also adjectives. As all other adjectives, thus, these must agree with the noun in number and gender: Tiene muchos problemas, bastantes preocupaciones y demasiadas deudas.

 B. FORMATION OF ADVERBS FROM ADJECTIVES

• To form an adverb add -mente to the feminine form of an adjective:

lento → lentamente rápido → rápidamente

feliz → felizmente difícil → difícilmente

 When used in a series, only the last adjective will add the suffix -mente:
Trabaja rápida y eficazmente.He works quickly and efficiently.

• The suffix -mente is rarely used with adjectives ending in -nte. Use adverbial phrases instead:

interestingly frequently intelligently elegantly more importantly

de manera interesante con frecuencia con inteligencia, de forma inteligente con elegancia lo que es más importante

• The common adjectives bueno and malo have their own corresponding adverbial forms:

(good) bueno → bien (well)	(bad) malo → mal (badly)
Ella habla bien el italiano, pero canta mal.