You domain is your site, it is say www.kevinstam.org. Your ISP is the internet service provider that you chose to lodge your domain at. It is their servers that become the holders of your site and where everyone who accesses your site goes. Moodle Partners provide fully serviced Moodles, and that service comes at a cost, which is why I have never setup a Moodle for myself on any service provider. Unless you have some organizational backing, one with funds, it is not a viable option, for me at least. One alternative is GoDaddy.com, but this is not a recomendation, and I have no idea what they charge. Shop around if you have a need for a site, but the cheaper the site, the less service you get, and that can be an issue of its own for a newbie.
Of course, if you have no imperative or serious business need for a Moodle and you really only want to learn about Moodle, looking to broaden your skills in this area, if you have a functional Moodle on your laptop, or desktop, use that. My setup in my home is I have 4 desktops and three wireless laptops. I have two Moodles on one machine, a v1.9.15 and a v2.2.1, those being the versions of the two small Moodles I admin and the one I my occasional employers use. All machines access the Moodles, and I use them to troubleshoot, to test stuff on, to create new course materials, to answer questions here mostly. But the v1.9 is going soon.