There is one Entries record for each combination of Person and Event. For Group events, such as team boats or relay races, there is still a separate Entry for each person in that group. The Entries within a Group are identified by setting the same Group value on all of those Entries for that Event. The Group values themselves are arbitrary, and can be reused for multiple Events.
After you have entered all of the Entries, you may need (or wish) to go back to the Schedule tab to redo the number of Races in some Events, scratch some Events, or otherwise fix up the Schedule.