Question

We would like to know the WordPress more about WordPress Category print and then print Post in selected category.

Like in this style

<h2>Categories Name 1</h2>
<ul>
<li>Post1</li>
<li>Post2</li>
<li>Post3</li>
<li>Post4</li>
</ul>
<h2>Category Name 2</h2>
<ul>
<li>Post1</li>
<li>Post2</li>
<li>Post3</li>
<li>Post4</li>
</ul>

Answer 1

WordPress provides a function to return all categories (get_categories()) and a function to list all posts of a category (WP Query object).

With the combination of the two, you can create the output you would like to do. The following is some example code that can be extended / changed with the parameters you need:

$categories = get_categories();
foreach($categories as $category)
{
  printf('<h2>%s</h2><ul>', $category->cat_name);
  $posts = new WP_Query('cat='.$category->cat_ID);
  while($posts->have_posts())
  {
    $posts->the_post();
    echo '<li>', the_title(), '</li>';
  }
  print '</ul>';     
}