Here is the code;

1st step:  Get your post from SQL

We will use sql command for get random post. Here is the command;

SELECT guid FROM wp_posts WHERE post_type = 'post' AND post_status = 'publish' ORDER BY RAND() LIMIT 1

Explaining of this command;

guid: The URL of our post

wp_posts: The table of posts

post_type: This is the type of we get

post_status: Is this published? Yes

order by rand: Randomize of our request

Limit: We limited for 1 post.

2nd Step: Locate the php code where you want.

<?php
$randomPost = $wpdb->get_var("SELECT guid FROM $wpdb->posts WHERE post_type = 'post' AND post_status = 'publish' ORDER BY rand() LIMIT 1");
echo '<a href="'.$randomPost.'">Random Post</a>';
?>

You can add this code where you want.
That’s All. Have a nice day!

Here is the code;

<?php if(isset($_COOKIE['comment_author_'.COOKIEHASH])) {
	$lastCommenter = $_COOKIE['comment_author_'.COOKIEHASH];

	echo "Welcome Back ". $lastCommenter ."!";

	} else {

	echo "Welcome, Guest!";
} ?>

That’s All. Have a nice day!