This code is located in the 'Publish' tab of your form. The basic embed code on this page should work great for you, but if you have a more advanced Wordpress setup you may need to visit the 'Embed Code' area of the 'Publish' page to view your options such as removing jQuery, jQuery UI, Modernizr, or CSS. More information about embedding your form can be found here.
Copy the code to your clipboard.
Step 2) Access your Wordpress.org site (http://yoursite.com/wp-admin/)
In order to add a form to your site, you must be an Admin, Editor, or Author.
Step 3) Create a new post
From the Wordpress dashboard, click 'Posts' > 'Add New'.
There will be a 'Text' tab on the right side of the post box.
Click it, then paste the code from Formstack into the text box.
Step 5) Preview and Publish
Now it's time to preview your page. If you like how it looks go ahead and publish it!
Note: Sometimes Wordpress themes have some CSS that overpowers the form. This can make the form look different than what it looks like when you previewed the form. You can override any changes the Wordpress theme made by editing the CSS of your form.