Hi ...
Your question is very vague, and to get anyone worth their salt to help, would require you to provide further information. A WebMailer can be achieved in many ways, and one contributor tried to steer you in the right direction, by asking a few basic questions that you failed to answer! If you are New to the Game, I would personally adopt a well tried amd tested Mailer, and would always - for Security Reasons - go for a Perl/CGI solution, and you could not do better than to do a quick Google search for the Free FormMailer by Matt Wright - downloaded by Millions of Users WorldWide.
I write all my own scripts, both Perl and PHP, which are tailored for the exact requirements needed at the time, but if you are a novice, and it sounds as if you are, you would be best served by the above advice ...
pELUKi