Every Fission App gets a free subdomain.
Currently, these look like
YOURUSERNAME.fission.name, but we're migrating to user accounts and attached apps, where every app has
To use a custom domain of your own, like
YOURAPPDOMAIN.com, you need to point your domain at our name servers in your domain registrar control panel.
Go to the domain you want to host on Fission in your Namecheap admin:
Where it says "Namecheap BasicDNS", select "Custom DNS" from the drop down:
ns2.fission.systems and click the green check mark to save.