Show Me is a special menu on the top-right of the toolbar. You can easily spot it with the 
icon. If you click on the icon, you can open and close a list of all the predefined Show Me visualizations.
In the Show Me menu, you can see 24 visualizations. If no fields are selected in your Data Source, all the options are gray. If you choose one or multiple fields (using Ctrl or Command), you'll see that some options are now available and one of them will have an orange outline (it's the one that Tableau advises you to choose). To use an option, click on it.
Let's do a quick example using Sample - Superstore:
- Simultaneously select Order Date, Category, and Profit in the Data pane
- Open the Show Me menu
- Click on some of the options to see different results
Show Me is useful when you start in Tableau, and when you have no idea how to visualize your data. You can click on the various options to see different results and use the one you prefer. After some time, you'll use Show Me very rarely. That's because, even if you have many possibilities, you are limited by how Tableau arranges the pill.
The automatic ways of building visualizations are fast and easy, but quickly limited. Do you remember the very first visualization you did in this book? The next screenshot will refresh your memory:
There is no way to create this visualization in an automatic way, either with double-clicks or with the Show Me menu. That's why you need to understand where to put the fields manually to create what you want.