iCal (also known as iCalendar or ICS) is a specification that allows people to subscribe to calendars that are maintained by someone else.
Google Calendar supports iCal, allowing you to subscribe to many publicly available calendars. Doing this adds an additional calendar to your account which you can view at any time. Just find the iCal link of the calendar you wish to subscribe to, then follow Google's instructions for adding a calendar using a link.
Here are some examples of how to find the iCal link for certain calendars:
St. Norbert College Master Calendar
Master Calendar provides information about many events on campus, including academics, alumni, arts, entertainment, lectures, religious, etc. Their iCal feature allows you to create a single custom link which contains events from only the calendars you're interested in. On the Master Calendar home page, click on "iCal Feeds" and follow the instructions from there to get the http link.
St. Norbert College Sports Schedules
On a sports team schedule page (i.e. football), right click on the small ICS icon, and select "Copy link address" (or other similar option) to get the link.
Other Calendars and Sports Team Schedules
Many K-12 school districts and sports teams publish their calendar of events. While viewing a calendar on any website, look for a link labeled something like "ical" or "ics" or "download" to get the link. Or you may need to contact the person in charge of the calendar and ask them if they have an iCal link available.
Note that the events on any calendars that you subscribe to are not included in your free/busy schedule. So if you plan to attend such an event, we recommend that you copy that event to your main calendar. This way others will know you're busy when they try to schedule a meeting with you. To copy the event to your calendar, click on the event, then select "Copy to my calendar".