Programming in general can be divided into two main categories. Things that you can see. Things that you can not see.
Things that you can see are like a Website, like the YouTube Website, this page you are reading this article on, the Yahoo weather app or Facebook messenger app. The parts that you see and can interact with, the Facebook Like button, Instagram filters and other visual pieces, all fall under what we call front end. Because it's in front of you! It's the front end of any application.
But where is the Yahoo app weather information comes from? That data is coming from an application that is written in a program that you can't see. Where your bank account information is stored and is not visible to the public can only be reached by you after you enter your username and password. That's the type of programming that is not visible. That is called back end programming. Because it's happening in the background.
Those are just some examples. Some other types of programming are teh database layer which kind of falls under back end. Quality Assurance (QA) and testing. You can actually write programs that will test other programs (mind blown). AI, artificial intelligence, self driving cars and things like Amazon's Alexa. There are other categories and types of programming but for the most part these are what you use to build the amazing apps you use every single day.