WHY PHP NO WORK

DEAR PROG

WHY NO WORK?
SICP WAS NO HELP.

url_setopt($curl, CURLOPT_POSTFIELDS,"name_f="$_POST["username1"]");
url_setopt($curl, CURLOPT_POSTFIELDS,"name_l="$_POST["username2"]");
url_setopt($curl, CURLOPT_POSTFIELDS,"pass0=$_POST["pass"]");
url_setopt($curl, CURLOPT_POSTFIELDS,"pass1=$_POST["pass"]");
url_setopt($curl, CURLOPT_POSTFIELDS,"email=$_POST["email"]");

>>3
"name_f=$_POST["username1"]"
How do I nested quotes?