Orcid connects you to external databases and visa versa. You have to grant permission for the external database to connect to your data, so you can choose. There are three types of external databases.
The "push" and "pull" external databases
The most useful once are that can "push" and "pull" from and to Orcid. One of such an example is the Europe Pubmed Central database. My favourite workflow is to import new publications into Orcid using European Pubmed Cental database. This results into an Oricd entry that contains a link to the European Pubmed database. If you click on the entry in Orcid, you are directed to the corresponding entry at the European Pubmed database. At the bottom of the entry you will then find your orcid ID and if set up properly with your name you get a list of all publications in the databases and their citation counts, really cool.
Overview of some of the databases that can be connected to your Orcid ID
Below you find a list of databases and funding agencies that can work with your Orid ID an their properties.