On a beau dire: It's like "we may say this as much as we want, it's not true." Example: "On a beau dire que les français sont élégants, ils portent parfois des vêtements horribles." "We may say that french people are fashionable, sometimes they wear some awful clothe." "On a beau dire que Jean est adorable, je le trouve méchant." "We may say that Jean is lovely, I think he is mean." On a beau faire: Close meaning, but used for actions. "On a beau travailler beaucoup, on ne gagne pas beaucoup d'argent." "We may work a lot, but we don't earn a lot of money." "On a beau [something we say or do], [something opposite to what would be expected]." Hope that helps!

To simplify Anna's good answer, it means "there's no point"/it's useless". If you took those words from the song "Amen" by Mickey 3D: - On a beau dire, on a beau faire, tout ce qu'on peut pour tout gâcher it means "try as hard as you want" (to spoil everything) but it won't work"

ça veut dire,c`est en vain de faire quelque chose ,,c`est ta dire ,n`importe quel effort tu fait ,tu ne peut pas réussir ,c`est comme de battre l`eau