The PS4 beta starts July 18th for people who pre ordered (you get a code from amazon/best buy/gamestop/etc that you have to redeem on bungie.net). The xbox one beta starts July 19th for pre orders. The beta is COMPLETELY open starting July 21st to all ps4/xbone users. The beta ends July 23d, no more beta until the game launches Sept 6th. Its not like D1 where they had alphas and 2 or 3 rounds of betas, but everyone will have 2 full days of beta access on consoles.
The PC beta won't be till august and it wouldn't surprise me if they cancelled it completely.
beta trailer - sounds 1 like story mission, 1 strike, and some PVP maps