Provided you've gotten yourself a beta code--the easiest way is to preorder the game--you can redeem it on Bungie's website. Assuming you select either the PS4 or PS3 version as your platform of choice (your beta code gets you access on only one system), you should now have access to three download codes through Bungie's website (and by email) so that you and your friends can dive right in.
Bungie's website is currently experiencing technical issues. Likewise, Sony's support website currently lists the PlayStation Network's status as "intermittently available"--likely as a result of the Destiny beta's launch. "The PlayStation Network is currently experiencing high volume and users may experience issues when connecting to the service," the page states. "We will update you with any changes that may occur in regards to this issue. Thank you for your patience." We've contacted Sony regarding the issues and will report back with anything we learn.
Bungie has not yet decided if progress from the beta will carry over to the final game. However, if you play the beta after 8PM Pacific on Saturday, July 26, you will receive an exclusive emblem for use in Destiny when it's released on September 9.
The beta runs from now until July 27 at 11:59PM Pacific, though it will be offline on July 21 and 22. Xbox One and Xbox 360 owners will be able to join the beta on July 23 at 10AM Pacific.
If you're taking part in the Destiny beta, what platform will you be playing on? Let us know in the comments below.