Note: This article provides steps for code provided by third-party sources. Any troubleshooting with third-party applications should be handled by the application’s support team or your custom developer.

You can add a pop-up to your website by using Jotform, a third-party form builder software. When creating a form on Jotform's platform, you are not required to add any form fields; you can simply add text or images in a pop-up window to announce sales, promotions, or a call-to-action.

You can create a Jotform account and build a form for free. However, Jotform limits how many times a pop-up can be viewed per month on their free version. If your form is on your home page, then you can easily surpass their monthly view limit. You may need to subscribe to their Bronze or Silver subscription. Here is a full list of the subscription options, along with their monthly view limit.

1. Create your Jotform account (or sign in if you've already created one).
2. Build a new form and add your verbiage, images, or design. 
3. Enable the pop-up functionality. This article from Jotform walks through how to enable the pop-up setting on your form.
4. Once you create the form, you will be provided with an HTML code to embed the form on your website. You will paste that embed code within an HTML Block on your website. See here how you can create an HTML Block to add the embed code.