Almost everything on the marketplace will come with instructions on how to use it.
If you want to learn how to build a website using the Portal Engine with web parts and widgets, you might want to start with reading through the documentation. If you have more specific questions then you should ask them here.
If you want your site to be responsive, that comes down to the markup you have for the site. If you have nothing, depending on what you want, you could use the responsive landing page template from the marketplace, otherwise you are going to have to design your own.