Apple made sweeping changes in iOS 7 and left few stones unturned in the core system apps that ship in the OS. Another app that saw some profound changes is the Calendar app, which was the recipeint of a significant visual overhaul.
Gone is the grey-blue look in the iOS 6 version of the Calendar. Replacing it is a bleached white UI that is accented only by the black text, red navigation elements and color markers highlighting important dates. Though striking, it is minimalist to the max and my be jarring to users expecting the color splash that graces the iOS7 homescreen. The layout is easy to figure out with the calendar in the middle and controls at the top and bottom. The top controls allow you to switch from a day view, month view and year view. There's also a search button and a "+" button to add a new event. The bottom lets you jump to the current date, select which calendars to view and and an inbox to view your invitations.
Year, Month, Week and List Views
The year view lets you see the 12-month calendar (shown at the top) and is useful for only cursory looks at the dates ahead of you and those behind. Tapping a month in the year will open the month view. The month view (also shown at the top) lets you see the most information in one location, but it gives you more of an overview of your agenda instead of the details. This is a significant change from iOS 6, which showed you the daily event details below the month.
The current day is marked in red, while days with events are marked with grey circles. You can easily scroll from month to month by swiping up or down. When you tap on a day, you are brought to the day in the day view.
The best view in the iOS 7 Calendar is the day view (shown below) which shows your daily schedule as well as the next seven days in a top navigation bar. A red dot highlights the current date when you are viewing it, while a black dot marks the date the you are viewing. You can tap or scroll to another day and your hourly schedule will appear underneath that day.
There's also a week view (shown below) that is only accessible when you turn your phone in the landscape orientation. Each event is highlighted in your schedule and includes the name of the event, so you can easily see what you have to do. You also can swipe up and down to view your daily schedule and swipe left or right to change the weeks.
Unlike iOS 6, which had a dedicated button for an agenda-style list view, the list view in iOS 7 is hidden. As noted by Steve Sande, you can see a list of your appointments by tapping on the Search icon at the top and searching for all events. You can see it in action in the video at the bottom of this post.
The create an event, you must tap on the red "+" symbol at the top right corner of the screen. This symbol is available in the day, month or year view. Still present is the ability to long tap on the screen to add an event, which was present in earlier versions of the calendar. Event creation is similar to iOS 6 with the same fields present in both versions of the OS. The layout in iOS 7 is slightly different with a stylish wheel-selector for the starting and ending dates/times, as shown below.
The Calendar app has been overhauled to match the minimalist design of iOS 7. As a result, a few key features like the month detail view. It's a toss up as to whether all the changes are bad or good -- a few features have been removed, but the clean look makes its easy to view your daily appointments and navigate the app. Like the other core apps, the Calendar is great for meeting your basic needs. If you want a bit more, check out Calendars 5 from Readdle or CalenMob.
Update: Updated to clarify the long-press to add an event is still available.