Insert record with PHP Prepared Statement

<?php
//create connection object
if(isset($_POST["btnSubmit"])){	
	$emp_id=$_POST["txtEmp"];	
	$revenue=$_POST["txtRevenue"];
		
	$db=new mysqli("localhost","root","","test");
	$stm=$db->stmt_init();
	$stm->prepare("insert into sales(employee_id,revenue,trans_on)values(?,?,now())");
	
	
	$stm->bind_param("sd",$emp_id,$revenue);//sd mean consecutive input as string and double datatype
	if($stm->execute()){
	 echo "Successfully Saved";
	}
	
	/*
	$emp_id='100';
	$revenue=400.00;
	$stm->bind_param("sd",$emp_id,$revenue);
	$stm->execute();
	
	$emp_id='101';
	$revenue=200.00;
	$stm->bind_param("sd",$emp_id,$revenue);
	$stm->execute();
	
	$emp_id='101';
	$revenue=300.00;
	$stm->bind_param("sd",$emp_id,$revenue);
	$stm->execute();*/
	
	$stm->close();
	$db->close();
}
?>
<form action="#" method="post">
<div>
Emp ID<br/><input type="text" name="txtEmp" />
</div>
<div>
Revenue<br/><input type="text" name="txtRevenue" />
</div>
<div>
<input type="submit" name="btnSubmit" value="Submit" />
</div>
</form>