From time to time, Microsoft releases updates for Dynamics 365 CE to fix issues or release new features. In the case of Dynamics 365 CE Online, Microsoft takes care of installing any updates for their customers, whereas in the case of the on-premises version, we need to install these updates based on our Dynamics 365 CE version. The following screenshot provides a list of the updates available for Dynamics 365 CE on-premises at present:
You can see a full list of Dynamics 365 CE updates at https://support.microsoft.com/en-gb/help/3142345/microsoft-dynamics-365-onpremise-cumulative-updates.