How to add a webform

Hi everyone!

Just wondering whats everyones best advice is for adding a webform to our website. We would like to be able to book appointments from our site and have it sent to our email. Being able to have the same client sign on several times and book appointments with custom fields, I have added web forms and they do not work, I get the msg “already subscriber” unable to process request on the ones I have tried out.. any ideas or suggestions?
Thanks in advance!