Database: Registration
Table = People
Records: id, name, gender, and phone
index.php
<form method="post" action="index2.php">
<input type="text" name="pesquisar" placeholder="pesquisa"><br>
<input type="submit" value="Pesquisar">
</form>
envia.php
<?php
$servidor = "localhost";
$usuario = "root";
$senha = "";
$dbase= "exemplo";
$conn = mysqli_connect($servidor, $usuario, $senha, $dbase);
For your file send.php, I assume you already know how to run queries in PHP. If you do not know, you can ask here or refer to the class mysqli of PHP (which is a good way to connect to MySQL database).
You can use the function LIKE of MySQL . An example is below.
$query = "SELECT * FROM pessoas WHERE nome LIKE '%".$pesquisar."%'";
Suppose the user typed ari in the HTML field. MySQL will fetch any name that has the ari substring. So, names like M ari a, ari ssa, M ari ana, Ari ane, Saf > ari will appear in the results.
You can perhaps improve your search by first searching for records whose fields have the same value as the searched, that is, only exactly what the user searched; then what to start with what the user searched; then, which ends with what the user searched; and, finally, what to contain what the user searched for.
One way to do
$pesquisar = $_POST['pesquisar'];
$column = "nome";
$querybase = "SELECT * FROM pessoas WHERE ".$column." ";
$query = $querybase." = '".$pesquisar."';"; // Os que são idênticos ao pesquisado
$query .= $querybase."LIKE '".$pesquisar."%';"; // Os que começam com o que o usuário pesquisou
$query .= $querybase."LIKE '%".$pesquisar."';"; // Os que terminam com o que o usuário pesquisou
$query .= $querybase."LIKE '%".$pesquisar."%' AND ".$column." NOT LIKE '".$pesquisar."%' AND ".$column." NOT LIKE '%".$pesquisar."';"; // Os que possuem o que o que o usuário pesquisou excluindo os que começam e os que terminam (já pesquisados).