In the Content Management section of the platform you can make content templates for all forms of messaging found on the platform.
Click on a content type to create a new template and you will be taken to the content screen for that channel, as it appears when creating a campaign. For example if you click In-App message you will get the full In App Message Content editor as shown below:
Saved templates appear in the List of existing templates and can be edited, duplicated or deleted as needed. You will be able to select your template when adding content for a channel when creating a campaign as shown in the example below: