You didn't load jQuery!
And you loaded the jQuery-migrate plugin twice! (Do you actually need it?) I see the documentation does show jQuery-migrate being loaded. I am skeptical about any plugin that requires jquery-migrate! Usually it is abandonware, but I see slickslider was last updated a month ago. You might query the author as to the need for jquery-migrate.
Load jQuery first, before any plugins.
The documentation for SlickSlider is poor in at least one regard: in some places, it doesn't show jQuery being loaded. I guess the author assumes users will know they need to load jQuery first. (But if you scroll down, it does show jQuery being loaded.)
USUALLY, "theme" files should be loaded before base CSS files. But that is just common convention. SlickSlider might be different - refer to it's documentation for proper CSS load order.