No credit card is required.
Go ahead and try things out. No pressure.
Group creation is not currently open to the public.
To create a group, requires an invite code.
A good group name should find a balance between being descriptive, fun, terse, memoriable and unique.
If your group is brand new, don't sweat this too much as you can change the name later if needed.
In the long run we encourage our groups to setup their own domain but to get started you can pick a custom subdomain.
Like your name, this can be changed later.