PHP Code:

 <?php
 // set your infomation.
 $dbhost='localhost';
 $dbusername='elsport';
 $dbuserpass='c4daa19';
 $dbname='elsport_users';
 // connect to the mysql database server.
 mysql_connect ($dbhost, $dbusername, $dbuserpass);
 mysql_select_db($dbname) or die("Cannot select database");
 
 //Are they just getting here or submitting their info?
 if (isset($_POST["username"])) {
 $username = $_POST["username"];
 $password = $_POST["password"];
 $cpassword = $_POST["cpassword"];
 $email = $_POST["email"];
 //Was a field left blank?
 if($username==NULL|$password==NULL|$cpassword==NULL|$email==NULL) {
 echo "A field was left blank.";
 }else{
 //Do the passwords match?
 if($password!=$cpassword) {
 echo "Passwords do not match";
 }else{
 //Has the username or email been used?
 $checkuser = mysql_query("SELECT username FROM users WHERE username='$username'");
 $username_exist = mysql_num_rows($checkuser);
 
 $checkemail = mysql_query("SELECT email FROM users WHERE email='$email'");
 $email_exist = mysql_num_rows($checkemail);
 
 if($email_exist>0|$username_exist>0) {
 echo "The username or email is already in use";
 }else{
 //Everything seems good, lets insert.
 $query = "INSERT INTO users (username, password, email) VALUES('$username','$password','$email')";
 mysql_query($query) or die(mysql_error());
 echo "The user $username has been successfully registered.");
 ?>

that is my code for the registration page, but on the page this part shows up in text above the form 0|$username_exist>0) { echo "The username or email is already in use"; }else{ //Everything seems good, lets insert. $query = "INSERT INTO users (username, password, email) VALUES('$username','$password','$email')"; mysql_query($query) or die(mysql_error()); echo "The user $username has been successfully registered."); ?>



could someone help?

I don't think your server is set up with php. Either that or you haven't named the file with a .php extension. The browser sees the <?php at the start and the > just before the 0 as the beginning and end of a big html tag.
You need to have php installed correctly and the file named with .php extension (or your server set up to parse html files as php).

Also (this isn't your problem) but you use | for logical or when you should use || instead. Logical or is for boolean values of true and false, eg true || false == true. | is bitwise or for numbers eg Binary 10001 | 01100 == 11101