get_option function

I'm currently trying to make my own theme, but i'm not quite sure how the get_option() function works, because how come this..

echo get_option('show_header', 'sultenhest_theme_display_options');
echo get_option('sultenhest_theme_display_options')['show_header'];

..both returns 1 (but Dreamweaver doesnt like the second option). While

echo get_option('twitter', 'sultenhest_theme_social_options');

..simply returns 'sultenhest_theme_social_options', which is incorrect.

An option would be to define the array as such

$social_options = get_option( 'sultenhest_theme_social_options' );

and call it like this

echo $social_options['twitter'];

It returns the correct string, but it only works in the header.php (if the array is defined there) file and not in, e.g. footer.php.