A custom event is an event with a name and set of parameters that you define so you can collect information that's specific to your business. For example, you could create a
donate custom event for when someone donates to an organization.
Before you create a custom event, review the list of automatically collected, enhanced measurement, and recommended events. These types of events automatically populate prebuilt dimensions and metrics and don't impact the limits on the number of events and parameters you can create.
Set up custom events
See custom events in Analytics
To see your custom events in Google Analytics, you need to create custom dimensions and metrics for the custom events and parameters.