Where should I put the iFrame code in my website?

Hi, I want to know where to embed this iframe code? Do I have to embed in designer CSS? 

I haven't embedded my form anywhere I'm just using it here. 

To embed your form you need to have a webpage or something, if you do not have a website and you want to use the form with the direct link you can do it.

Where you need to put the iFrame code will depend on the platform you used to built your website, you should find the section to embed HTML code and paste the iFrame code there.

You may also provide us which tool you used to built your website, we will be glad to assist you embedding your form.