Adverbs
Spanish adverbs are relatively simple and similar to those found in English. e.g. muy ("very"), poco ("a little"), lejos ("far"), mucho ("much, a lot"), casi ("almost"), etc. To form adverbs from adjectives, the adverbial suffix -mente is generally added to the feminine singular of the adjective, whether or not it differs from the masculine singular. Thus:
claro ("clear", m. sg.) → clara (f. sg.) → claramente ("clearly")
rápido ("fast, rapid", m. sg.) → rápida (f. sg.) → rápidamente ("fast, quickly, rapidly")
natural ("natural", m. & f. sg.) → naturalmente ("naturally")
triste ("sad", m. & f. sg.) → tristemente ("sadly")
audaz ("bold", m. & f. sg.) → audazmente ("boldly")
The important adjectives bueno ("good") and malo ("bad") have irregular adverbial forms: bien ("well") and mal ("badly"), respectively.
A few adverbs are identical to their adjectives. For example, words such as temprano ("early"), lento ("slow"), and hondo ("deep") can be both adjectives and adverbs (there is no change in their spelling).
If there is a series of consecutive adverbs that would each end in -mente on their own, the -mente is dropped from all but the final adverb, and the others are left as if they were adjectives in the feminine singular. Thus:
rápida y fácilmente = "quickly and easily"
lenta, cuidosa, y duchamente = "slowly, carefully, and skillfully"
parcial o completamente = "partially or completely"
There are also many adverbial phrases in Spanish, such as a menudo ("often"), en todas partes ("everywhere"), de repente ("suddenly"), por fin ("finally"), and sin embargo ("however, nevertheless").
As with adjectives, the comparative of adverbs is formed by placing más ("more") or menos ("less") before the adverb. Thus más temprano ("earlier"), más rápidamente ("faster, quicker, more quickly"), menos interesantemente ("less interestingly"), etc. The superlative iis formed by placing the neuter article lo before the comparative, although it is generally used with an additional qualifier phrase such as que puedas ("that you can") or de todos ("of all"): lo más rápidamente que puedas ("as quickly as you can", lit."the most quickly that you can"), lo más interesantemente de todos ("most interestingly of all"), lo menos claramente de ellos ("the least clearly of them"), etc.
Source: https://en.wikipedia.org/wiki/Spanish_grammar#Adverbs