Configuring account sync and display options
You can configure background data use and synchronization options for all of the applications on your phone. You can also configure what kinds of data you synchronize for each account. Some applications, such as Gmail and Calendar, have their own synchronization settings.I would highly recommend the user manual to all users.
Some applications, such as Contacts, Gmail, and Calendar, can sync data from multiple applications. Others sync data only from the first Google Account you sign into on your phone, or from an account associated specifically with that application.
For some accounts, syncing is two-directional; changes that you make to the information on your phone are made to the copy of that information on the web. Your Google Account works this way. Other accounts support only one-way sync; the information on your phone is read-only.