Embedding your Mailchimp forms into your Showit site is really simple.
First log into Mailchimp and select Audiences, then Set from the many options to specify the audience settings: https://mailchimp.com/help/change-audience-name-defaults/
From here you can use the form builder to build out your forms. Once you have the form you want to add to your site created, choose the embed forms option.
Once you're on the embedded forms page it will look like this. Choose your form type (red), edit form options (blue), see the preview of your form (green), and once you have it dialed in copy your embed code (yellow).
Once you have your form embed code copied head over to Showit, select the canvas you want to add the form to, and choose the embed code option as shown below.
Then click inside the "custom code" box in the right sidebar once you've added the embed element to your canvas and paste your code into the box that pops up and click save.
Issue: May cause slight initial delay loading other content on the page appearing to make things glitchy.
Solution: This can be resolved by adjusting the embed code and adding a small async="" text to the code in the proper place. See the image below for placement.