While previewing your event, your talk/s are not showing up on your page.
Here's a quick fix to check your talk settings:
Is the talk Active?
Check by heading to Content > Talks.
If there's a red exclamation mark next to the Talk record, it's not Active.
Click on the ... next to the Talk's record.
Click on Advanced Settings > Visibility and tick the 'Is Active?'
This will need to be ticked for every talk you want to be available.
Now if you've checked the Talk is Active and it's still not showing on your public site, you'll need to check your Speakers are Active.
Take note of the Speakers attached to your Talk
Head to Content > Speakers
Click on the '...' next to their record and select Manage Speaker.
If you see that the Active box is un-ticked, you should tick it.
Make sure all of your Speakers for that Talk are Active.
Your Talk will now appear on your summit's public site.