Summarize:

" This phrase means "happy birthday" and is used to greet someone on their birthday. It is suitable for anyone in any situation. Pronounce "feliz cumpleaños" fay-LEEZ KOOM-play-ahn-yohs.  You can add the name of the person or their relationship to you if you feel so inclined. For example, if you were wishing happy birthday to your mother, you might say "¡Feliz cumpleaños, mi madre!" If you want to say "happy birthday" in a more informal way to a friend, you can also say "feliz cumple" (fay-LEEZ KOOM-play). "Felicidades" (fay-lee-see-DAH-days) means "congratulations." While it may seem odd for you to tell someone "congratulations" on their birthday, it's a common birthday wish for Spanish-speakers. This is especially appropriate if you've already wished the person a happy birthday once.  For example, if you were attending a friend's birthday party, you might say "feliz cumpleaños" when you arrived, then say "felicidades" as you were leaving. You can also say "felicidades en tu día," which means "congratulations on your day." On someone's birthday, it's common to wish them a long life or express the hope that they celebrate many more birthdays to follow. If you wanted to express this sentiment in Spanish, you would say "¡Que cumplas muchos más!" A literal translation of the phrase would be "that you complete many more." Pronounce it "kay KOOM-plahs MOO-chohs mahs." The basic Spanish birthday song uses the same tune as the song in English, which you may already be familiar with. However, the Spanish lyrics don't necessarily translate directly to the lyrics in English.  The lyrics for the basic Latin American birthday song are: "¡Feliz cumpleaños a ti! ¡Feliz cumpleaños a ti! Feliz cumpleaños querido/a (name), feliz cumpleaños a ti. Ya queremos pastel, Ya queremos pastel, aunque sea un pedacito, pero queremos pastel." In Spain, on the other hand, you would sing "Cumpleaños feliz, cumpleaños feliz, te deseamos todos, cumpleaños feliz."
Say "¡Feliz cumpleaños! Use "felicidades" to express general congratulations. Tell the birthday celebrant you hope they have many more. Sing the "Happy Birthday" song in Spanish.