How to get the Theme directory path to the current theme?

I think you have to be a little careful because it depends on what you are trying to do.

If you are using a child theme get_template_directory(); will still go to the parent theme. However get_stylesheet_directory(); will go to the current theme, child, or parent. Also, both these functions return absolute server paths.

If you wanted a fully formed URI, for links or images, you should use get_template_directory_uri(); or get_stylesheet_directory_uri(); using the correct one for the reasons stated.

Summary
get_stylesheet_directory()
absolute folder path of current theme
e.g. /var/www/yoursite/wp-content/themes/child_theme

get_template_directory()
absolute folder path of parent theme
e.g. /var/www/yoursite/wp-content/themes/parent_theme

get_stylesheet_directory_uri()
full URL of current theme
e.g. https://example.com/wp-content/themes/child_theme

get_template_directory_uri()
full URL of parent theme
e.g. https://example.com/wp-content/themes/parent_theme