Hey Samantha,
Option 2 where you use the php function “do_shortcode()” would need to be inserted between the opening and closing tags of the element you want to display it inside of. For example:
<div>
<?php echo do_shortcode( ‘[instagram-feed]’ ); ?>
</div>
If you want to put the feed in the header like you mentioned, this would go somewhere in the header.php template file for your theme.
The php tags (in bold) before an after the function are not necessary if you use the function inside a block of php code. An error has the potential to “white screen” your site and lock you out so be very careful and get help from someone familiar with php code if at all possible.
Let me know if you need any more help with this!