You can load in your own HTML code for your campaign by creating a new message through the blue Create New Project button (assuming you are on the main SimplyCast page after you have logged in). Follow the wizard and choose to create your project from a New Design.
As you follow the steps of the Wizard, you will be asked to select a template. If your design has a layout already defined and you don't want to use one of our templates, choose the Blank Template.
You will then reach the message editor. Here, you can load in your HTML code by switching to the HTML view. The icon to show the HTML view is labeled Source. Click on it to switch to the html view.
You can then copy and paste in your HTML code into the editor. If you need to edit the content before you save the message, click on the Source button again to return to the normal editing view.