By default, Events in your site cannot be viewed by others unless they are logged into you site. It's assumed that organizations may primarily use Events for internal training not privy to the public.
If, however, your organizations would like to let people see your Events without being logged in, you have the ability to do so. This may be helpful if you would like to promote trainings to individuals not yet within your site.
To do so, go to Site Building, then under Social Features toggle Front-Facing Events to On.
Then go to Events and go to an Event you would like to share externally. Simply copy and paste the URL to others, who can now view it without being logged in.
Individuals can then log in or register an account, and then register for the event if applicable.