Have your stoney mail e-mail address name and password ready.
Start with step 1.
The Permissions of the OpenSync app need to be changed, so that the calendar and the contacts can be synchronized.
Press on the app for a while and a menu will appear. Click on "App info" to get to the "App info" menu.
There, click on "Permissions".
It's possible that your menu will look a bit differently. This is the case, as the UI may vary between Android versions. It is important that you still follow these instructions, even if your settings app may look a bit different.