First, you need to know that "song lyrics" in Spanish is translated as "letras de canciones".
The word "letras" means "letters". And that is how lyrics are referred to in Spanish.
Go to any popular search engine such as Yahoo or Google and next type in the name of the artist and the word for lyrics.
For example:
Juanes letras
or
Maná letras
This will bring up sites with lists of the song lyrics of the group you searched for.
Likewise you could type in the name of the song (in Spanish) and then type in "letras". That should bring up the song that you want.
This will bring up the sites that have lyrics for the popular Colombian singer Juanes.
If you want to start at a site, there are some Spanish lyrics sites in the resource section of this article. Just click on one of the links.