It's jut that this is not set:

$_SESSION['nama'];

The piece of code you posted, is not showing how $_SESSION['nama']; is initialized.

how to set it? this is my full code:

<?php
session_start();
$nama =$_SESSION['nama'];
require('fpdf17/fpdf.php');

$connection = mysql_connect("localhost", "root", "");
$db = mysql_select_db("qurban", $connection);
$query = mysql_query("select * from pengguna where nama='$_SESSION[nama]'", $connection);

while($rows=mysql_fetch_array($query))
{

//A4 width : 219mm
//default margin : 10mm each side
//writable horizontal : 219-(10*2)=189mm

$pdf = new FPDF('P','mm','A4');

$pdf->AddPage();


//set font to arial, bold, 14pt
$pdf->SetFont('Arial','B',14);

$pdf->Cell(189,5,'',0,1);//end of line
$pdf->Cell(189,5,'',0,1);//end of line
//Cell(width , height , text , border , end line , [align] )

$pdf->Cell(140,5,'YAYASAN SALAM MALAYSIA',0,0);
$pdf->Cell(69,5,'INVOICE',0,1);//end of line

$pdf->Cell(189,5,'',0,1);//end of line
$pdf->SetFont('Arial','',12);

$pdf->Cell(140,5,'',0,0);
$pdf->Cell(30,5,'No. Rujukan',0,0);
$pdf->Cell(19,5,$rows['id_pengguna'],0,0);
//make a dummy empty cell as a vertical spacer
$pdf->Cell(189,5,'',0,1);//end of line



$pdf->SetFont('Arial','B',12);
$pdf->Cell(10,5,'',0,0);
$pdf->Cell(90,5,'Pegawai,',0,1);
$pdf->SetFont('Arial','',12);
$pdf->Cell(10,5,'',0,0);
$pdf->Cell(90,5,'No 22 Jalan Changgai,Pjs9,',0,1);
$pdf->Cell(10,5,'',0,0);
$pdf->Cell(90,5,'46000,',0,1);
$pdf->Cell(10,5,'',0,0);
$pdf->Cell(90,5,'Petaling Jaya,',0,1);
$pdf->Cell(10,5,'',0,0);
$pdf->Cell(90,5,'Selangor.',0,1);
$pdf->Cell(189,5,'',0,1);
//billing address
$pdf->SetFont('Arial','B',12);
$pdf->Cell(100,5,'Bill Kepada',0,1);//end of line

$pdf->Cell(189,5,'',0,1);//end of line
$pdf->SetFont('Arial','B',12);

//add dummy cell at beginning of each line for indentation
$pdf->Cell(10,5,'',0,0);
$pdf->Cell(90,5,$rows['nama'],0,1);

$pdf->SetFont('Arial','',12);

$pdf->Cell(10,5,'',0,0);
$pdf->Cell(90,5,$rows['alamat'],0,1);
$pdf->Cell(10,5,'',0,0);
$pdf->Cell(90,5,$rows['poskod'],0,1);
$pdf->Cell(10,5,'',0,0);
//$pdf->Cell(90,5,$rows['bandar'],0,1);
$pdf->Cell(10,5,'',0,0);
$pdf->Cell(90,5,$rows['negeri'],0,1);


//make a dummy empty cell as a vertical spacer
$pdf->Cell(189,10,'',0,1);//end of line



$pdf->Cell(138,5,'',0,1);

//invoice contents


$pdf->SetFont('Arial','',12);


$pdf->Cell(189,10,'',0,1);
$pdf->SetFont('Arial','',12);
$pdf->Cell(175,10,'*Sila bawa invoice sebagai bukti tempahan',0,1);
$pdf->Cell(175,10,'*Sebarang masalah atau cadangan sila isi borang aduan di Laman Hubungi Kami ',0,1);
$pdf->Output();
}?>

if i delete the database, pdf will come out...

how to set it? this is my full code:

This is your code, you are supposed to know what is this "nama", that you are storing in the user's session.

nama is my data inside my table pengguna in phpmyadmin

oh ya btw after i code $query = mysql_query("select * from pengguna where nama=$_SESSION['nama']", $connection);

it shows: Parse error: syntax error, unexpected '' (T_ENCAPSED_AND_WHITESPACE), expecting identifier (T_STRING) or variable (T_VARIABLE) or number (T_NUM_STRING) in

What is your PHP environment? What version of PHP is installed?

my php version is 5.6.31

nama is my data inside my table pengguna in phpmyadmin

Yes, but when you do

$nama =$_SESSION['nama']; 

It means that earlier you had

$_SESSION['nama']=...

The error you are seeing is being you are retrieving the value of $_SESSION['nama'], whereas it has never been set before.

my php version is 5.6.31

You need to switch to the PHP 7.2, because the 5.6 branch reaches its end of life on December 31th 2018, no more security support after this date.

ok i try it 1st