Syncing with Google Calendar
Using the calendar on an Android phone wouldn't be any good unless you could share it with your Google online calendar. This is actually the easiest way of keeping appointments and tasks straight. From Google calendar, you can have your daily appointments emailed to you or have them pop up on your Android phone, as reminders.
To sync with your Google calendar, you'll need to, of course, have a Google account. There are actually two ways to go about this - when you first set up your Gmail account (if you set up your phone to receive Gmail and you have a Google email account), you'll be asked if you want to sync both your contacts and your calendar. You can bypass both and set them up later. If you bypass this option, you can still have your Google calendar sync to your phone.
Once again, go to the settings menu. This is done by hitting the menu button on your phone -- settings will be in the lower right hand corner of your screen. Within settings, there are two different options for Google calendar sync - Calendars and Calendar Sync. Calendars allows you to select the different options you have set for your online calendar. For instance, if you have the weather or holidays that show up on your Google Calendar, you can have them show up on the calendar app. Calendar sync is where you sync your Google Calendar with the Android app.
I have two Google accounts and, though I use one more than the other, both are being synced to my Android phone. Auto sync allows for automatic changes to take place on your calendar. So if you make changes on your online calendar, they will be automatically updated on your phone.
One downside that I and other users have experienced is an issue with appointments that are made on the phone that don't seem to show on the online calendar, or at least it takes a while before they show. This of course is a major downside, especially if you use your Android to input appointments more than you do your online calendar.