Like many hosted website providers, we use CNAME records to provide custom domain support. CNAME works by telling an end-user's web browser to look at our domain (domains.launchkit.io) instead of the original domain they requested when they visit your hosted website address.
CNAME records are the best way to accomplish this kind of website hosting because it allows us to scale our offering with the most flexibility, without you having to update your DNS configuration. (This means we can potentially add many IP addresses around the world, change hosting providers, and do cool things like geo-targeted DNS, without any service disruption.)
The downside is that "naked" domains (ie. your domain without the "www.") don't typically work with CNAME, unless your hosting provider does something special behind the scenes to make it work. (Some DNS providers do this, silently translating a CNAME to a set of "A" records, or proxying requests for you.)
As a result, your naked domain should redirect to the subdomain you chose for your App Website, which can be accomplished easily using the most common DNS providers, or by using static hosting services like Amazon S3 for the naked domain.