For everyone doing the network security challenge (the VMs, not Cisco):
CyberPatriot Training Materials (might help also cisco people?)
Windows
Windows powershell videos
Check misc for war games to help you learn windows commands
Linux
Learn comamands
Command Line -- beginner friendly
Linux introduction -- interactive
VIM Tutorials
https://www.openvim.com/ -- interactive walkthrough
https://sites.radford.edu/~nokie/vim/spr19/beyond.html -- for reference
Hardening Guides
If you want to start practicing, you should use a virtual machine. VirtualBox is a good hypervisor(the thing that runs the vm) that works on Mac and Windows. Download a debian ISO here. Here's a tutorial on how to get started. You can do the same with a windows ISO to practice if you don't have a windows computer.
For Cisco challenge:
Cisco Resources (free):
Check networking section of topics you can look up