The only requirement for creating an event is that it have a name. In the context of importing constituents to an event, you need to have a value in the "Gen. Event Name" column/field.
NOTE: When loading gift records, you can associate gifts with events by using the "Gift Event Name" field.
It is also possible to have recurring events in LGL. Read the Recurring events or classes - how to record attendance Knowledge Base article for more information.