WishList Member (and CourseCure) are WordPress plugins so they can be installed and used on a hosted WordPress powered site. A copy of WordPress can be downloaded at any time from WordPress.org
Downloading and installing WordPress on your hosting account is a typical way to use WordPress and any available WordPress plugins. You can install WishList Member on a site running WordPress using the typical methods.
WordPress.com is a different environment as it is hosted by WordPress so if you go that route, you will just need to be sure you are using a WordPress.com account that allows for plugins to be installed.
WordPress.com offers packages for sites that do not allow for plugins or themes to be installed so WishList Member cannot be used on those types of sites.
A Business Plan package is offered by WordPress.com which does allow for the installation of 3rd party plugins and themes. So WishList Member should work as expected on a WordPress.com site that allows for plugins to be installed.
You can use the WordPress option that best suits your needs and allows for plugins like WishList Member to be installed.