It's been a while since I've read the Swarm documentation, but it was fairly comprehensive from what I remember. If you're referring to this tutorial[1], note that you don't need to use a cloud provider, and you can also do it with local VMs.
Actually you don't even need a cluster of machines. While Swarm can easily scale out, you can get started with a single machine and figure out the clustering later. Even on a single machine there are benefits of using Swarm over plain Docker (Compose): stacks, secrets, advanced networking. So you can test it out there and add more machines as you need it.
One thing I'd suggest is to first get familiar with Docker itself, since Swarm simply builds on these concepts and adds orchestration. Use `docker run`, understand volumes, images, permissions, user namespaces, cgroups, etc. Then move on to Docker Compose and get familiar with the configuration, services, etc. And then finally pick up Swarm, which even uses the same Docker Compose configuration file (with slight variations), so it should be fairly straightforward at that point.
Though honestly, learning Swarm in 2021 might not be a good investment, since Kubernetes is clearly the market leader, and I wouldn't be surprised to read a sunset notice about it, even though Docker Inc. is still supporting it. So you're probably making a good decision to stick with k8s.
Good luck!
[1]: https://docs.docker.com/engine/swarm/swarm-tutorial/
