To use it, you only have to configure your e-mail client (outlook, eudora...) so that you can use your own machine as a server. That is to say: the IP 127.0.0.1 in the configuration of the e-mail program you are using.
That way, the messages will be sent to your machine (to the program miniRelay) and this program will take care of sending it to the recipients.
Be careful with keeping the program always on, some viruses choose these applications to send themselves to other computers. Anyway, from its console you can see everything the program does.