I think subscribing means you sign up to receive a calendar from someone else. So the local Jr high has a iCal calendar of school events and we can subscribe to this, and it shows up on our calendar. Publishing means you are putting your calendar up for others to subscribe to.
So the apple dot mac site has some information. If you want your calendar to show up from a web browser, I think you need to set up a group. Then you publish your calendar(s) to the group. Apparently you can combine calendars into a group so you don't have to publish them separately.
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One-step calendar sharing
Choose the calendar you want to share and select Publish from the Calendar menu. Or use iCal to group related calendars, then publish them as one. You can select one of your published calendars to appear on the home page of any .Mac group you own. Friends and family can view your published calendars, too. Just send them the calendar URL and they'll be able to see the most up-to-date version of your calendar in day, week, or month view from any computer with an Internet connection.
