when ordering thru docker cloud web ui, where do services get deployed: which provider? Must we deploy nodes or node clusters prior to ordering services/containers?
I wouldn’t use the word “ordering” for your services, but I can put it simply for you.
You deploy nodes or node clusters either from Docker Cloud if your subscription is linked, or manually with Bring Your Own Node. When you have nodes managed by Docker Cloud, i.e they appear under “Nodes” in the menu, you can deploy services that run on these. You create a stack, a stack can consist of one or more services. A service can be scaled through a number of containers.
I suggest you take a look at the documentation to understand how everything works together: https://docs.docker.com/docker-cloud/