Many of the questions asked around here are already answered by the various forum FAQ lists, actually.
btw, may I suggest that your tutorials assume register_globals is off, as that is the norm?
It saves on newbies having to ask why the script doesnt work on their server, and is good practice anyway 🙂
You should also use isset() or empty() for an initial check of coming variables, rather than using something like:
if ($submit) {
straight away.
You might also want to consider formatting output statements as:
$message = "Name: {$yourName}\n"
. "Email: {$email}\n"
. "\n"
. "{$content}\n";
mail($sendto, $subject, $message, "From: {$email}");
or
$message = "Name: " . $yourName . "\n"
. "Email: " . $email . "\n"
. "\n"
. $content . "\n";
mail($sendto, $subject, $message, "From: " . $email);
though this would really be personal preference.