The best stories are done through BOTH telling and showing, to give the readers a unique experience and perspective. It's like fine cooking -- you can't say it has to follow the recipe to the T or whether you have to use X amount of salt vs. Y amount of sugar, etc. It's how all the ingredients come together...
However, when you're learning how to write, it's good to look at examples of show vs. tell.
In general, "show" is more exciting and detailed and enables the readers to actually experience your story instead of being told about something. But tell is great for speeding up the pace, or summarizing something that can be mundane if you show ("They had breakfast with eggs and ham and it was delicious" is perfectly fine to get the story going, instead of writing a long scene talking about the breakfast.)