The ability to define and use your own functions is part of what gives the Wolfram Language such power. It is often inconvenient to have to explicitly name a function for every small operation that you wish to perform. The Wolfram Language lets you declare functions inline (called pure functions) to get around this.
The most transparent way to define a pure function is with Function. The first argument is a list of arguments, and the second is a function. This function adds its two arguments together:
Pure functions become quite powerful when used together with Map.
You can use /@ as a shorthand for Map. Use a pure function to create a list of clickable buttons: