Read Franck Dernoncourt's answer to What is an intuitive way of explaining how the Fourier transform works? on Quora
Best graphic explanation about Fourier transforms
Alimento del Alma: Textos, Homilias, Conferencias de Fray Nelson Medina, O.P.
Alimento del Alma: Textos, Homilias, Conferencias de Fray Nelson Medina, O.P.