If you check the official website, you'll see that you also need a mailer the one that sends the emails. In most cases you just have to set up the mailer to use the built-in SMTP settings, and sometimes you need an IMAP or POP3 server. Unfortunately, Yahoo is not a solution since it doesn't offer this possibility. Gmail is a recommended solution for this. Gmail's limit is also 2000 sent per day so there shouldn't be a problem with that.
The password and accounts are defined in the source files that you use and are stored on the server that can't be accessed by users.
For additional info, read the info on the official website: http://www.bebosoft.com/products/formstogo/overview/