In order to apply to Expedia, go to Channel Manager > Marketplaces and locate Expedia on the list:
When hitting on Apply you will see this pop up:
Accept terms of Service, and you'll see that your Expedia module has changed:
If you click on Cancel the connection will be interrupted and none of your activities will be showing on their end.
If you would like to continue with the integration, hit on Manage.
A list of your activities will come up, for you to choose which ones you want Expedia to distribute:
Select the ones you choose and hit on save.
Within a couple of days, you'll receive an email from Expedia confirming the integration, and you'll start seeing your activities on their end. Here's a live example: