I was studying in a book called "Kihon no Kihon" on the web and programming, but the following code doesn't work.
Input form part

<form method = "GET" action = "return.php">
Name:<input type = "text" name = "username">
<input type = "submit" value = "submit">

echo "Hello".
$_GET ["username"]. "San";

The aim, when you send by entering hundred to form part, Hello but I likely to be returned to the hundred's, will be returned remains of the input content not reflected code. By the way http: // localhost: In the case of call direct 8888/return.php will be displayed only properly string in the form of "Hello's".
The environment is mamp visual studio code, and both codes are stored in htdocs.