Can I create a popup window for my Pressero site?

Pressero itself does not have functionality at this time for creating popup windows to be added to the sites.
But popups for sites using HTML, Javascript and CSS can be created in many different ways. Just searching for 'popup generator' will return a great many sites that provide generators to create popups, and popups can be created manually by a programmer familiar with HTML, Javascript and CSS.
An example of a very basic popup modal window added to the long description for a product on a site is shown on the image below.
The code for this popup was added to the Product > Long Description area using the insert code button </> and pasting in the code for the popup into the window that comes up.
The code for this popup is shown below:
<script>window.confirm("Pay attention to special shipping options!");</script>
Although this example of a unstyled modal window may not be preferable in it's style, it does highlight the concepts of adding a popup to a Pressero site. This example shows the code being added to a product, but a popup could be added to the Settings > SEO / HTML area of a site under the HTML content for top of <head> section, the HTML content for bottom of <head> section, or the HTML content for top of <body> sections on that site settings window. Code added to that area would be applied to all pages on the site.
Alternately, the code for a popup could be added to a page created on your site. In this case, the code for the popup is added in the page content tab, also using the insert code </> button. A popup added in this manner would only be displayed when the page itself was actually viewed on the site.
The code to create a popup can be very different depending on the site, the styles used on the site or in the popup, the goal of the popup and the behavior that it should display. If you are interested in having us create a custom popup window for you, please open a ticket at to Professional Services and we can discuss creating a popup for your specific needs.