Every person that is added to Eventsforce will have a "personal details" page created for them along with a "person ID". Generally, this person ID is tied to the user's unique email address.
There are various ways to access the "personal details" page for a user. Two commonly used methods are running a search and through the "Registrations" page.
Accessing the 'Personal details' page through a search
This method is best used if the person has not yet registered for an event, but exists in Eventsforce through an imported list or as an abstract/award submitter.
Go to Reports > Quick Search
Enter the email address of the person
Check "Search all events"
Click the "i" icon the left of the person
Accessing the 'Personal details' page from the registration list
This method is best used when the person has already registered for an event.
Go to People > Registrations within the event this person exists in
Click the "person" icon to the right of the attendee's row OR select the record, then choose "Edit person..." from the tools drop-down