What is it called when you sing without words?
A cappella (singing without instrumental accompaniment, sometimes accompanied by a chorus of nonsense syllables)
What is it called when you sing a song?
A person who sings is called a singer or vocalist (in jazz and popular music). Singers perform music (arias, recitatives, songs, etc.) that can be sung with or without accompaniment by musical instruments. Singing is often done in an ensemble of musicians, such as a choir of singers or a band of instrumentalists.