In order to publish Email messages and Email Campaigns into your channel, you'll first need to create those assets in your library. To learn how to do this, refer to the two articles: Composing & Sending Email Messages and Adding messages to your Library.

Publishing Emails
Click your channel icon and then 'Manage Channel' icon on the right of your header, then 'Manage Library.'

Click the 'Add New Media' and then select 'Email Message' to open up the "Choose Email Message from your library" interface. Select the email message you wish to add.

Select the appropriate channel to publish the message to. You may also add or choose tags, schedule the publish/expiration date of the email message, and  select if users should be allowed to edit the message. Then select the green 'publish' button.

Publishing Campaigns
To publish an existing Email Campaign from your library, follow the same steps above, but instead of choosing 'Email Message,' select 'Campaign.'