Usage of the Slick-Modal for TYPO3
First you have to create a content element, which you want to display within the Slick-Modal. This content element can be placed in a record container in your pagetree. Allowed are all variants of tt_content records. That means that you're also able to place plugins within your Slick-Modals.
Afterwards navigate to the page, where you want to use a Slick-Modal. Create a new content element of type Slick-Modal and select the content element to show. Within this Slick-Modal content element, you're able to select a Preset which defines how your Slick-Modal is embedded. Read more about that in section Presets.