a phrase chiefly used in northern England.
it is a contracted form of "it'll be reet", where "reet" means "alright" or "OK".
living your life according to "be reet" is the only way to find happiness in life.
Geoff: "ZOMFG a just hopped off the buz n me 'ouse is burnin' down n me Deirdre's in there dyin!"
Jack: "Be reet."