This process is somewhat technical and involved, but we are happy to help if there are any questions.
First build a form in FormStack.
Go to Publish then Advanced.
Copy HTML code into a basic text editor. (Notepad on Windows or TextEdit on OS X)
Look for the three lines of FormStack CSS and copy them just before the closing </head> tag on the page with the FormStack form. This last bit is somewhat technical, so you might want to talk to us or your site admin for help. The screenshot below is for HubSpot, but will be different from user to user.
Locate where you want the form in the HTML on your page and add "<div" followed by a space.
Run 'Find' for <body, and copy part of the body tag after the "<div" tag.
Copy everything between <form... and the end of the "img" tag (after the closing form tag, and paste it following the div tag.
Add </div> following the previous code.
Then Save and you should be all set.