1. Open the → Android system settings, scroll down to the menu item → Accounts and click on it
2. Click on → Add account
3. Choose the account type you want to add (e.g. Google as highlighted in the screenshot below)
4. Enter the account information to set up your account. For Google accounts you can also create a new one here
When you successfully have entered the account information, your device and Business Calendar are ready to communicate with the newly added account. If the auto-sync functionality of your device is enabled, it will start to pull the information of this account from the servers.
To synchronize with another account type just choose your favorite one similar to screenshot #3. If the desired account type is not available on your device, it may be possible that you have to install the corresponding application first.
Hint 1: If you already added the account for sync and experience some problems syncing the calendar, please verify if your Android Stock Calendar has the same issue. If yes, it might be a general sync error and it might help to remove and re-add the affected account to your device. If you have problems syncing an Outlook/Exchange account, you may also want to check this article.