Hi, Laravel doesn't comes with a UI or a pre-made theme like Wordpress.
The main difference is because Wordpress is a CMS and Laravel is a framework, which means Laravel can be used for any application you want to build, even a CMS (like https://octobercms.com/ ).
With this in mind, if Lavarel had pre built UI/themes for pages, single content, etc. this might be useful to you but not to others.
For your projects you can choose a library (like Bootstrap or Bulma) or a template and adapt the html to your needs.
For the last question an admin theme is basically a template to use in the background of your applications, in this case there are some libraries (like https://voyager.devdojo.com/ ) to help you manage your application. But again the backend will be some functionality only available to some users, so you can build from the ground up following your specific needs.
I hope I made myself quite clear.