There are two main ways to put a calendar on your site. One is to use a calendar plug-in. If you find a plug-in that you like and that works well with your site feel free to install and use it. However, keep in mind that SNO does not provide support for third part plugins.
The second methods is to embed a Google Calendar. To embed a Google Calendar, you'll first need to create a calendar in Google and then get the calendar's embed code. Then you'll need to either create a page or a widget on which to house the the calendar. If you choose to create a page, then you'll embed the calendar on that page by placing the embed code in the Edit Page box while it the Text tab is selected. Then you'll probably also want to place a calendar tab on your navigation bars. If you choose to display it in a widget, use the SNO Embed Code widget to display the feed. Simply paste this entire embed code into the SNO Embed Code widget, and click Save.