ofcourse, ready-made scripts are easiest because it saves you a lot fo work, but it also means you'll never learn how to do it yourself.
Read the PHP manual about the mail() function.
That should let you send mail in the first place.
Values entered in a form are automatically available as global variables in your script, so that shouldn't be a problem.
Read the php manual section about filesystem functions
to learn how to open files and read the content.
At the most basic level you can just uuencode the data from the file and append the uuencoded data to the body of the email. Modern methods use mime and all that cr*p, but good old UUE is a lot simpler to use.
At presto, files attached to emails.