Where do you get the embed code?

On the Form Builder you only need to click on the Publish icon. 

A window will appear there you will be provided with a code that you only need to copy and paste in your website. 

Here is also a guide about it: http://www.jotform.com/help/34-Adding-a-Form-to-a-Web-Page. 

This other guide will help you to decide which embed code to use: http://www.jotform.com/help/67-Which-Form-Embed-Code-Should-I-Use.