1. Look in mail.php ... you can open it with notepad. Around the 6th line it tells you what version you have, and you should have version 1.9.4
2. I'm assuming that you are using this walkthrough right here http://www.scriptsearch.com/cgi-bin/jump.cgi?ID=3402 and this is where you got confused.
3. Based on the walkthrough, we want to edit config.php only not mail.php.
4. Here are the things you want to edit:
$subject = "Simple PHP Form Mailer";
[What the email will be called in the subject line when you receive it]
$mail_to = "firstname.lastname@example.org";
[This is where the message will go once the user hits send]
$from = "email@example.com";
[If you create a form where there is no option for the user to enter their email address (which means you can't reply to them) it will show the email address you enter here as the sender... you can make this the same email address as the previous field (mail_to) above]
$error_repote = 0;
$error_page = "error.html";
$send_page = "thankyou.html";
$error_msg = "Sorry, Error Sending Email!";
$ok_msg = "Thank you, Email was Sent!";
[OK, if you keep the top line ZERO (0), you have to enter an error_page and send_page value (a valid html page), because whether the forms fails or succeeds, it will forward the user to either a confirmation or error page. If you change the value to ONE (1) you don't have to bother with the forwarding pages, because it will just pop up the message(s) you define in error_msg and ok_msg]
$blank_error = "Sorry, cant send if the form is blank !";
[This is the error message that will show when someone tries to submit a blank form (nothing filled in)]
$image_error = "Sorry, Image Validation Failed !";
[The message that shows up if the imagine validation is not correct... basically if they enter the wrong code]
$email_error = "is not a valid e-mail address !";
$field_error = "field is blank, this is a mandatory field !";
[The first line checks whether the user entered a valid email address... if they didn't, the email_error message will display. The second line is if they leave ANY OTHER field (besides email field) blank that you set as mandatory.]
$form_names = array("name", "email", "comm");
[Here is where you set which field are mandatory. When you setup the contact form, each field HAS to have a unique name... in this line you enter all the field names that are required by you.]
$img_validate = 0;
[Turn image validation on or off... ONE (1) is on and ZERO (0) is off. Remember that if you turn it on, it requires probably some extra steps that can be found here http://onetforum.com/formmailer/img_validate_howto.txt]
$send_reply = 0;
[This line is if you automatically want to send the user who used your contact form an auto-reply. ZERO disables auto reply and ONE enables it.]
$reply_email_subject = "Thank your for using Simple PHP Form Mailer";
$reply_email_from = "firstname.lastname@example.org";
$reply_email_form_name = "Simple PHP Form Mailer";
[These are only require is you have send_reply enabled]
PS: The reply_email.txt file is the message you define that is going to be sent to the user automatically.
OK, once you've set all the variables... create a HTML page with a contact form, at least a name field, email field and message field and try it out. Remember that based on the configurations all the files config.php, mail.php, reply-email.txt (if you have it enabled), and img_include.php (if you have that enabled), error.html & thank you.html (if you chose to forward the user to a page once form has been submitted) HAVE to be in the same folder as your contact form page.
Hope this helps.