The easiest way to perform a synchronization between multiple devices is using the same sync-account and add it to the Android system settings of your devices (normally under →  Accounts and Sync). While adding the account to your Android device, please make sure that you set a checkmark behind →  Sync calendar (here some more detailed information on how to add an account for sync). If you want to view the → Birthdays on various devices, please make also sure that you set a checkmark behind →  Sync contacts in the list. The birthday information is read out from your contacts.

When it comes to sync of task lists across various devices, you need to make sure the same account is added as well. Please find more detailed information here.

After a short first synchronization everything should be available on all devices, if they have a consistent internet connection. Please also check if the Auto-Sync feature has been enabled on the devices. You can find detailed instructions here.

If you set up the devices correctly and still have sync issues, you can resolve here.