It's an adverb that describes something that is done or happens with little difficulty.
Here are some examples of how to use "facilmente" in a sentence:
* Puedo hablar español fácilmente. (I can speak Spanish easily.)
* El niño aprendió a leer fácilmente. (The child learned to read easily.)
* Se puede llegar a la playa fácilmente. (You can get to the beach easily.)