Step 1: Download Google Calendar Sync
Syncing Google Calendar with Outlook is a simple as installing Google Calendar Sync, a small software utility which allows the two to talk to each other. The utility can be downloaded free of charge directly from Google.
DOWNLOAD GOOGLE CALENDAR SYNC
Once the installer has been downloaded, run it and follow the on-screen instructions.
Step 2: Configure Google Calendar Sync
The first time you run Google Calendar Sync, you'll be asked to input your username and password, and to configure how the application will sync the data between Google Calendar and Outlook:

Make your selections and click "Save." That's it! You're done:

General Use
Google Calendar Sync will continue to sync with Outlook based on the choices you make until you indicate otherwise. The utility sets itself to run each time Windows starts, so you don't have to worry about manually starting the program.
An icon for the Google Calendar Sync utility sits in your Windows Taskbar. To check the status of the syncing process, just let your pointer hover over the icon:

The best part for Windows Mobile users is that changes made in Outlook, Google Calendar or the Windows Mobile Calendar are all synced with each other for one complete time management solution. If, for example, you add an appointment on your Windows Mobile device, then sync your handheld with Outlook, the new appointment will be stored on the handheld as well as in Outlook and Google Calendar; the same is true for entries made directly in Outlook or to Google Calendar.