Adding custom column to default post table

//defining
add_filter('manage_posts_columns', 'dct_table_head'); //use manage_{$post_type}_posts_columns for custom post type
function dct_table_head( $defaults ) {
    $defaults['column1']  = 'Column1';
    $defaults['column2']    = 'Column2';
}

//configuring data
add_action( 'manage_posts_custom_column', 'dct_table_content', 10, 2 ); //use manage_{$post_type}_posts_custom_columns for custom post type
function dct_table_content( $column, $post_id ) {
    if ($column == 'column1') {
    //do your stuff here
    }
    if ($column == 'column2') {
    //do your stuff here
    }
}