Is there any article that tells the difference and relationship between KVM, QEMU, libvirt, virt-manager, Xen, Proxmox etc. with their typical use cases?
In really simple terms, so simple that I'm not 100% sure they are correct:
* KVM is a hypervisor, or rather it lets you turn linux into a hypervisor [1], which will let you run VMs on your machine. I've heard KVM is rather hard to work with (steep learning curve). (Xen is also a hypervisor.)
* QEMU is a wrapper-of-a-sorts (a "machine emulator and virtualizer" [2]) which can be used on top of KVM (or Xen). "When used as a virtualizer, QEMU achieves near native performance by executing the guest code directly on the host CPU. QEMU supports virtualization when executing under the Xen hypervisor or using the KVM kernel module in Linux." [2]
* libvirt "is a toolkit to manage virtualization platforms" [3] and is used, e.g., by VDSM to communicate with QEMU.
* virt-manager is "a desktop user interface for managing virtual machines through libvirt" [4]. The screenshots on the project page should give an idea of what its typical use-case is - think VirtualBox and similar solutions.
* Proxmox is the above toolstack (-ish) but as one product.
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[1] https://www.redhat.com/en/topics/virtualization/what-is-KVM
On the first path you are likely going to be just fine with VirtualBox, VMWare Workstation or Hyper-V (Windows only) / Parallels (Mac intended). Which one you should pick depends on your desired use of the machines.
On the second path you would go with a solution that deals with the nitty-gritty details, such as Proxmox, oVirt, Hyper-V, ESXi, or any of the other many available options - granted you are not going full cloud-based, which opens up a whole lot of different options too.
You would generally never need to worry about which components are needed where and why. I've had to worry about it once or twice before, because I've had to debug why an oVirt solution was not behaving like I wanted it to behave. Knowing the inner workings helps in that case.
As a Linux user, why would you want to use VirtualBox or VMWare Workstation? They are not so well integrated with the system, and, frankly, VirtualBox is more of a toy VM player... just go for virt-manager. It gives a conceptually similar interface to VirtualBox, but better integration with the rest of the system. Especially, when it comes to stuff like sending different key combinations.
I honestly cannot think of a single benefit to using VirtualBox (and I'm less familiar with VMWare player) compared to virt-manager. My guess is that it's more often used because it's also a common choice on MS Windows, so, you get more hits if you are going to search the Web for questions associated to VMs / you'd get tutorials for how to set up a VM that use VirtualBox. But, if you apply yourself to learning how either one of these works, you'd see no reason to choose it.