One of my favorite SharePoint features - in both SP2007 and SP2010 - is the ability to have calendar information included on your site. There are some limitations, but we'll save that topic for another day.
For this example, i'll be using SharePoint Server 2007 (a.k.a. MOSS) and Office 2010 - but this would apply if I were using Office 2007 as well; the interface would just look slightly different.
Let's say you're in charge of a resource room and you want to keep a calendar that includes reservations for that room for any given point in time. You can create a calendar within SharePoint to do this. That's great, because you can easily publish it in such a way that the appropriate "audiences" can see the calendar to know if it's booked.
Assuming you have designer privelages for the site in question (like a MySite), click the "Site Actions" tab (upper right corner), then click "Create".
From the create menu, under "Tracking", you'll see an option called Calendar. Click that to open up a new Calendar item.
Now you'll see options to customize the new Calendar item - Name, Description, Quick Launch, and - if your administrator has enabled it - the "Incoming Email" option. This option allows you to create an internal email address for the calendar, which would in turn allow you to forward items to the calendar by emailing them.
After clicking "Create", you'll see your new calendar within the SharePoint site. You now have the ability to do things like change permissions (who can see the calendar), creating other views of the calendar (like a spreadsheet), adding items, setting up RSS feeds, alerts, etc.
Another option, under the "Actions" tab, is "Connect to Client". This will allow you to synchronize the calendar with Outlook - which enables you to do things like view the shared calendar side-by-side with your existing Exchange-based calendar.