Route parameters capture segments of the URI and pass them to your controller. There are required and optional parameters:

// Required parameter
Route::get('/user/{id}', function ($id) {
    return "User ID: $id";
});

// Optional parameter
Route::get('/user/{name?}', function ($name = 'Guest') {
    return "Hello, $name";
});

// Regular expression constraint
Route::get('/user/{id}', function ($id) {
    //
})->where('id', '[0-9]+');