Almost always your host, ISP or whatever will have a 'mail relay' that you can use. That is, you just need to put in the hostname of that in Moodle's SMTP setting. This is usually the most likely thing to work. Just ask your network administrator for the details of your mail relay. Only if that fails do you need to start understanding how mail is configured.
I remember the first time I built an MTA from scratch myself - lots and lots of stress