Explain me this plz

Question

<?php
$v="var1";
Echo $v;
$$v="var2";
Echo $$v;
Echo $var1;
?>

Answer 1

echo $v = echo "var1" = var1

$$v = "var2";

$var1 = "var2";

echo $$v = echo "var2" = var2

echo $var1 = echo "var2" = var2