Inserting a user sign-up record using mysqli
Like it was said in the comments, this code needs not a review but just some basic practices. That said, good basic practices are a rare specimen in the wild, so you cannot be blamed, given the number of awful tutorials out there. Luckily I am the renowned collector of good practices and here you are

Connectivity

There ate many things that could be improved in your connectivity file. To name a few


the connection character set must be configured to avoid issues with characters
the proper error reporting mode for mysqli must be set
the connection error smust be not bluntly echoed out


All these issues are covered in my article How to connect properly using mysqli: so let's take the code from there:

$host = '127.0.0.1';
$db   = 'webchat_data';
$user = 'root';
$pass = '';
$charset = 'utf8mb4';

mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
try {
    $conn = new mysqli($host, $user, $pass, $db);
    $conn-&gt;set_charset($charset);
} catch (\mysqli_sql_exception $e) {
     throw new \mysqli_sql_exception($e-&gt;getMessage(), $e-&gt;getCode());
}


Password hashing

In two words, never store passwords in plain text. Use password_hash() function instead. This topic is thoroughly explained in the question: https://stackoverflow.com/questions/1581610/how-can-i-store-my-users-passwords-safely 

Prepared statements

Just never add a variable to SQL query directly, but mark its place with a question mark instead. Then bind the actual variable and finally call execute()

In detail this matter is explained in this question: https://stackoverflow.com/questions/60174/how-can-i-prevent-sql-injection-in-php

So here is your signup code reviewed

&lt;?php
include 'connectivity.php';

$uname = $_POST['uname'];
$email = $_POST['Email'];
$pass  = password_hash($_POST['Password'], PASSWORD_DEFAULT);

$sql = "INSERT INTO `sign-up`(USERNAME,EMAIL_ID,PASSWORD) VALUES(?,?,?)";
$stmt = $conn-&gt;prepare($sql);
$stmt-&gt;bind_param("sss", $uname,$email,$pass);
$stmt-&gt;execute();

header("Location:index.php");