In the Manage Guestlists Tab, you will need to click the Create New Guestlist At This Venue which is located at the bottom of the window.

A new page will be displayed called Create Guestlist At 'venue name'

The Guestlist requires a name, date and time. After entering these values and saving the list, a new page will be displayed showing the 'Attendees on this Guestlist' box.

You can either add attendees from a spreadsheet, copy/paste the names or add them one by one.

By clicking on the 'Import Attendees From A Spreadsheet' button, this pop up will be displayed: 

This is where you can Copy/Paste the names and Upload from an excel spreadsheet.

To Upload a spreadsheet, you will need to download the provideed AttendeeList.csv This is available when you select the 'Upload Spreadsheet' tab

After the names have been entered, make sure you Update Guestlist under the description of the Guestlist.