In the OS X Calendar, at least up to OS X Mountain Lion, the way to move from month to month, or week to week, is to hit the right or left arrows near the top of the calendar window, a fairly typical mechanic among calendar apps, really.
In OS X Mavericks beta, however, you can move through them much more intuitively. Here’s how.
Launch Calendar on your Mac running OS X Mavericks beta, and bring up the Month View. Now, instead of hitting the right or left arrows to move one month at a time, simply scroll up and down to continuously see the next or previous weeks.
The name of the month you’re viewing will still show up on the right side of the Calendar window so you won’t get confused, and the current week will have a red line across the top of it as an easy visual cue.
Leave it to Apple to keep refining and updating even basic apps like Calendar. Yay!