A very common requirement is to have a variable route parameter (or more) that gets used by the code that maps to the route, for example, the ID or path alias of the page you want to show. These parameters can be added by wrapping a certain path element into curly braces, like so:
path: '/hello/{param}'
Here, {param} will map to a $param variable that gets passed as an argument to the controller or handler responsible for this route. So, if the user goes to the hello/jack path, the $param variable will have the jack value and the controller can use that.
Additionally, Drupal 8 comes with parameter converters that transform the parameter into something more meaningful. For example, an entity can be autoloaded and passed to ...
