There's an overview of the new features at comiXology's website, but the gist is this:
- Subscriptions: when you go to a title's main page, you can subscribe by clicking on a button under the main image that says "subscribe to series." Issues will be delivered and auto-debited to the credit card you have on file when they become available. You won't get collected editions, back issues or even the current issue when you subscribe--your first "automatic" issue will be the next one, and you will be alerted to when that issue will hit when you click to subscribe.
- Bundles: Called "curated collections" in the description, bundles of comics can be sold for cheap, allowing fans to pick up a number of comics and get started on them all at once. Marvel, Image, Valiant, Monkeybrain and more have subscriptions available already, and if they turn out to be big hits you'll surely see DC, BOOM! and others follow suit.
- For iOS, they're also rolling out a fit-to-width and two-page display function, giving more options for how readers can view their content and putting their app on a bit more level playing ground with the comics that you buy directly to your Nook and Kindle, both of which have done that natively almost since they started supporting comics but neither of them have comiXology's depth of library.