You’ll need to create a custom block to contain the javascript and anchor required for embedding a Twitter timeline.
The Custom Block Manager is found in User Home → Journal Manager → System Plugins → Generic Plugins → Custom Block Manager.
Once a custom block is created, you can add the content via User Home → Journal Manager → System Plugins → Block Plugins → “Your Custom Block Name”
The content is positioned in Journal Setup Step 5.6. User Home → Journal Manager → Setup → The Look → Journal Layout.