I have a website http://sharenotes.xyz/.
In this website users can save and share quick notes to others users.
There is a unique note id for each note. (id can only contain [0-9A-Za-z_] charachters).
Unique note id is present in the url http://sharenotes.xyz/hithere.
In this case hithere is the unique note id.
In actual the url is like
http://sharenotes.xyz/index.php?id=hithere.
My folder structure looks like -

and index.php file is present in public folder.
What will be the content of the .htaccess file to short the url from http://sharenotes.xyz/index.php?id=hithere to http://sharenotes.xyz/hithere and in which folder should I place that .htaccess file ?
I know php but I am new in htaccess file (stored in public_html folder).
UPDATE
I was forget to tell you something that -
There is folder named as public which servers all user accessible files.
So I have also hide the name public from the url throught .htaccess file.
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteRule ^$ public/ [L]
RewriteRule (.*) public/$1 [L]
</IfModule>
Options -Indexes
That's why you wouldn't see public in url.