theming – working on Custom Slider Programmatically and want to print twig file’s code in block

I am working on a custom slider programmatically. I create a Custom Module (block_example) and make a block (BlockExample.php) and a twig file (blockexample.html.twig) and also a module file (block_example.module). I want to place some code in twig file and call it in block file.

this is build function frome block file (BlockExample.php)

public function build() {

    $renderable = (
    '#theme' => 'blockexample',
    );

    return $renderable;
}

this is (blockexample.html.twig) file code
     <div class="col-sm-3">
        <h1>This is Title</h1>
        <p>Description Coming From Twig File</p>
     </div>



this is (block_example.module) file code
function block_example_theme() {
  return array(
    'block_example' => (
      'variables' => ('test_var' => NULL),
    ),

  );
}

Now main question is how to print twig file in BlockExample.php