What you are dealing with is a relationship issue that must be resolved before you design a layout to work with your data. You have what is called a "many to many" relationship. A given contact can be involved in many events. And a given event can have many involved contacts. Those contacts may be paid or volunteer staff who will organize and run the event and they can also be the guests that attend the event. They might even be major contributors that are sponsoring the event, but they can all be contacts linked to a given event.
Start with these relationships:
Events::__pkEventID = Contact_Event::_fkEventID
Contacts::__pkContactID = Contact_Event::_fkContactID
You can place a portal to Contact_Event on the Events layout to list and select Contacts records for each given Events record. Fields from Contacts can be included in the Portal to show additional info about each selected Contacts record and the _fkContactID field can be set up with a value list for selecting Contacts records by their ID field.
For an explanation of the notation that I am using, see the first post of: Common Forum Relationship and Field Notations Explained
For a demo file that just so happens to match contacts to events and that illustrates a number of layout design options for working with a many to many relationship download this file: https://www.dropbox.com/s/oyir7cs0yxmbn6i/ManyToManywDemoWExtras.fp7
This demo file was created in the older file format so people using FileMaker 12 or newer should use Open from FileMaker's File menu to open this file and produce a copy converted to the newer file format.