This example shows a Bootstrap Modal.
Note 1: you need Bootstrap & Bootstrap Modal for this example. Download it from here:
http://getbootstrap.com/javascript/#modals
Copy the JS- and CSS-file into your fileadmin-folder!
Or better: install a Bootstrap extension and you are done!
Note 2: if you want to copy this HTML-file to your fileadmin-folder, you can specifty the folder like this:
plugin.tx_camaliga.view.templateRootPaths.1 = fileadmin/template/files/
Copy this file in a subfolder named "Content" of this folder.
Note 3: use the field "custom1" for the modal-button/link or change the template.