If you want to sync your calendar between your phone and tablet, you just need to use the same Google account. By doing this, all your data, including calendar will be sync between the two devices. If you are using different accounts, just add one account to the other device. This can be done by going to Menu > Settings > Accounts and sync > Add account. After you finished adding the account, connect your device to the Internet and tap on Sync all button from the same location.