Trade After Hard Brexit: WTO Rules Explained

There has been a lot of talk about World Trade Organisation rules coming into force after Brexit. These are the rules and principles which would guide the UK's trade relationships after leaving the EU. So what will trade be like for the UK after Brexit and how will operating under WTO affect the UK?
Brexit Explained Playlist: goo.gl/8VNcEi
EU Single Market Explained: goo.gl/eRLvoY
EU Customs Union Explained: goo.gl/UKjjjd
EU Free Trade Area Explained: goo.gl/ZbukzP
What Will Happen to the UK After a No Deal Brexit?: goo.gl/abfRmS
Hard Brexit Explained: goo.gl/FaLjvD