Help Using Google Calendar on Android

The Google calendar that appears on the Android calendar widget is that which is associated with the Google account tied to the phone.

Any "friends" or other calendars shared to that account will have events visible on the calendar widget.

From a PC, log into the google account and access the web calendar. Then choose "Other calendars" and "add a friends calendar" to add events from other calendars. These will appear under the calendar widget on the Android phone too once synced.