how to active featured image

how to active featured image in custom template word press

 

Didn´t Hefaistos advice you in the previous thread? It´s like this:

in your functions.php file

if ( function_exists( 'add_theme_support' ) ) {
add_theme_support( 'post-thumbnails' );
set_post_thumbnail_size( whatever-size, whatever-size, true ); 

PHP:

And then in your loop:

if ( has_post_thumbnail() ) {
    the_post_thumbnail();
}
the_content();

PHP:

this is all in the wordpress codex.