Frontend form add data to database

Hi

I’m building a custom plugin to capture customer data.
I have a function that, when called from the front, shows the form – like this (simplified for sake of brevity):

function plugin_form() {
?>

<form name="customer" method="post" action="">
	<input id="name" name="name" value=""/><br/>
	<input id="surname" name="surname" value=""/><br/>
	<input id="email" name="email" value=""/><br/>
	<input type="submit" name="submit" value="submit"/>
</form>	

<?php
}

My plugin creates the appropriate database tables during activation.
I have this function to save the data:

function save_data() {
	global $wpdb;
		$name = $_POST['name'];
		$surname = $_POST['surname'];
		$email = $_POST['email']; 	

		global $wpdb;
		$wpdb->query = "INSERT INTO wp_plugin ('name', 'surname', 'email') VALUES ('$name', '$surname', '$email');";
		echo 'thanks';
}

The question is:

How do I get the form appearing on the frontpage to call the save_data function in the plugin file?

Any help would be greatly appreciated.

Thanks