networking

I would start with getting a good idea of how things actually work, like the TCP stack, DHCP, Wifi, etc. Learning these basics will help a lot in diagnosing issues, because you'll be able to isolate it to specific parts of the network to look at. Having a good grasp of the basic principles of networking has really helped me a lot in figuring out issues.

A lot of the other stuff - like "how do I configure wifi in the office" - is highly vendor-dependent. The process for, say, setting up a guest network is going to be different depending on what hardware you have. But if you have a good grasp of the basics of networking you'll be able to figure out what those settings actually do.

Sadly, I learned a lot of this stuff through trial and error and long frustrating attempts at getting wifi and routing and VPNs to actually work, so I don't have any materials to recommend.

Edit: Another tip is to be able to build models of the systems you're making so you can test changes. It's incredibly helpful to have an environment you can break and rebuild quickly to test things. This goes for basically everything sysadmin related.

Look up "CompTia Network+ course"

Watch everything in the "Power Cert" series, then watch everything in the "Professor Messer" series.

You won't get through everything in a month unless you are a really fast learner, but you can get through a large amount of content.

Complete both courses, and you will have a solid base level of understanding for computer networking.

The key things to know IMO:

1. The whole OSI model top to bottom for troubleshooting. If I ask you, "What's the difference between a layer 2 and a layer 3 switch?" You should be able to instantly answer.
2. Understand IP addressing well. Know what they are, why they work they way they do, and how they apply in a basic network. You should know what CIDR is.
3. Understand subnetting well. It will confuse you at first, keep watching videos on it until you actually understand it.
4. Know what DHCP and DNS are and how they are used in a network. This will be CRITICAL to effectively troubleshoot a network problem. A huge number of networking issues boil down to problems with DHCP, or problems with DNS.
5. Understand VLANs and how they are used and why they are important.
6. Understand network ports, memorize the most common dozen or so. Know what and how they work and why they matter for security.
7. Understand the basics of packet anatomy, what they are, how they are formed, packaged, sent, routed, received, unwrapped, and responded to.
8. Understand VPNs at a basic level and how they work. Know the difference between an IPsec implementation, an OpenVPN implementation, and an overlay network like TailScale. Understand why somebody would chose one over the others.
9. Practice basic commands and tools like ping, tracert/traceroute, and nmap. These are incredibly useful and necessary to troubleshoot connectivity issues. I use them on a weekly basis at my job.

That all should get you going. It's intimidating, but very rich and rewarding when you start to get it.

And of course, practice practice practice!!! You will NOT learn by just sitting in front of your screen and watching the videos. Get into the command line and start messing around. Grab an old tower or laptop, throw a Linux distro on there and play with SSH, ping, nmap, Uncomplicated Firewall (UFW), start opening and closing ports. Tell certain services like SSH to listen on different ports than the default port 22. Etc.

Get yourself a copy of TCP/IP Illustrated. It's old, but it's still relevant. The basic protocols haven't changed that much.

http://intronetworks.cs.luc.edu/

https://youtube.com/playlist?list=PLxbwE86jKRgMpuZuLBivzlM8s2Dk5lXBQ

Use available tools, what concepts are you stuck on?

https://www.freecodecamp.org/news/osi-model-networking-layers-explained-in-plain-english/