Here's how you setup your MailChimp/Shortstack integration and host a basic signup on Facebook.
- Log into your MailChimp Account.
- Get your api key, by going to Account > API Keys and Authorized Apps.

- Copy your API key.

- Open the Tab Designer in Shortstack.

- Click on the Newsletter Signup Widget under Add Widgets.

- This will bring up the configuration dialog. Now you'll need to enter your API key and click Get Lists.

- Select the list that you'd like to add to your Facebook page.

- Now you can setup any advanced options you'd like, including displaying instructions, terms and conditions or change labels.

- Save your widget.
Want to spice up your signup form? Feel the need to get creative? Here's how you create a Code Widget instead of the Signup Widget.
- Log into your MailChimp Account.
- Head over to your List tab. Click the formunder the list you want to use.

- Flip over to the share it tab and click on the Create HTML code for a small subscribe form.

- Configure your form's settings and save them. Then scroll down to the copy/paste into your site code, select all of the code and copy it.

- Now, head over to Shortstack and open your Tab Designer.

- Add a new Code Widget to your tab and paste your copied code there. (CTRL+V on Windows, Command+V on a Mac)

- Save your widget and you're done.

You can sign up for your own Shortstack account here. Need more help? You can get help and more from the Shortstack support team at shortstack.zendesk.com. They have a getting started help page and MailChimp how-to advice. There's even a demo video.