To add participants to your event, click on a specific event and then select the Participants module. You can then press on the Plus button at the top right of the screen to add a new participant. You will be able to add a single participant or upload a file of participants from your desktop.
To add a single event participant, select that option and fill in the required basic details (First name, Last name and Email address). When you are done, click on save and the participant will appear in the list of existing participants.