convert HTML theme to WordPress theme

Hello. I am trying to convert an HTML theme to a WordPress theme. I have create all the files neccesary and added the code . But, when I go to the site, It appears a white box in the header place. And when I use this api: <?php wp_head(); ?> to the header, this white box still appears, but the menu or the header appears only on half of the wide.
Can someone please show me how to remove that white box? I am not finding any solution

thank you