I remarkable way....
To my understanding what happens is the following
The mail and calendar items are saved in a database in the cloud of your mail service provider. Google owns the gmail, Microsoft owns live, outlook, hotmail. The database of the service provider is leading.
On your PC, laptop, tablet and or phone are email and calendar clients installed. When you configure these clients you have to enter your email address and password, with which they are able to access your mail and calendar items at your server provider.
When you start up a client it opens the server to synchronizing its contents with the server, when you enter a new item in a client, the same happens the other way around and the newly entered item is stored safely in the database of your provider..
When not all clients have the same content, I expect that they synchronize with a different provider, hence don't are configured with the same email address and password.