Login to the Dashboard of your WordPress site and select “Appearance”, then select “Widgets”.
Find a text box on the left side of the screen and drag it into the sidebar that your site uses, placing it in the position of your choice. I recommend that it be above the fold.
Paste the code into the empty text box.
Pimping Your Opt-in Box
You can give the text box a title, “Sign up for my Newsletter”, but I recommend instead that you leave it untitled and create a Call to Action with an image and words.
Special Tip: Go to “create a new post” and use the WYSIWYG editor to upload an image and write some text. Then place the html in the text box above the embed code.