Very simple example…
function sinan_customizer_register($wp_customize){
$wp_customize->add_section( 'section_name', array(
'title' => 'Text Title',
'description' => 'Text descripotion sometin hee'
) );
$wp_customize->add_setting( 'setting_name', array(
'type' => 'theme_mod',
'default' => 'default text here',
'sanitize_callback' => 'esc_attr'
) );
$wp_customize->add_control( 'control_name', array(
'label' => 'Text Label ',
'description' => 'Text descripotion sometin hee',
'section' => 'section_name',
'settings' => 'setting_name',
'type' => 'text'
) );
}
add_action( 'customize_register', 'sinan_customizer_register' );
and this is how you get your setting pick one;
get_theme_mod('setting_name');
echo get_theme_mod('setting_name');
$var = get_theme_mod('setting_name');
For more info check this: https://divpusher.com/blog/wordpress-customizer-sanitization-examples/
and this: https://codex.wordpress.org/Theme_Customization_API
and Check this out to understand layout
