From the website:
"After much experimentation, what we ended up with was a pack that came with fourteen objects, twelve of which were Magic cards (in contrast with a Draft Booster, which comes with sixteen cards, fifteen of which are Magic cards).
The goal was to create a booster that had a path that you went through as you opened it. Rather than just one excitement point, we designed the booster to have many excitement points. To do this, we've organized the booster into four sections that we're calling chapters (Welcome, Fireworks, Big Finish, and Epilogue), each with some number of cards that we're calling slots.
First up, I should tell you that Set Boosters are going to cost a little more than Draft Boosters, but because you have the opportunity to open more rares per pack (you can open up to four rares or mythic rares in a Set Booster—both wildcard slots, the rare slot and the foil slot—and that's not even counting The List), we expect that you will get the same number of rares and mythic rares per dollar spent as you would buying Draft Boosters.
Set boosters are going to come in 30 packs to a booster box display rather than 36.
The Set Booster has been designed to look very different from Draft Boosters, so you'll be able to clearly tell them apart. Here's what the Zendikar Rising Set Booster will look like..."
WEEKLY MTG EVENTS
WE ARE CURRENTLY HOSTING ZERO EVENTS
AT THIS TIME DUE TO COVID-19!
A special promo pack will be awarded to the winner of Draft!
A special promo pack will be awarded to the winner of FNM!
A special promo pack will be awarded to the winner of each event!