How Do I Start Learning About Computer Networks?

You can of course go to school for networking, but I’m assuming this question is what you can do on your own to better your knowledge.

Much as with other technical skills like programming, photography, or cooking, the best way to learn is by doing!  I would suggest setting up a network and start making it do different things and once you’ve figured out how to do those things, move on to larger scale projects.  For example, do you know how to setup your home network from scratch via the web interface?  If so, what about from the command line?    What about setting up a port forward manually so you can see something on your computer at home away from home. Attach some storage to your network somehow. Break your network into two parts with different IP schemes and bridge them, networks share a printer, host your own web domain, setup VPN to your home network so you can…  There are limitless opportunites to experiment. Each time you try something new it will be hard and you’ll probably break the entire network in the process, but that’s where the learning is because when you figure out WHY it broke and HOW to fix it, you’ve just leveled up!

Beyond experimentation with topology there are some very specific things you need to learn in order to make sense of how networks operate and for those I would seek out both books and ask questions on networking forums.

Learn how IP address work.  Why are they assigned the way they are?  Who/what assigns them?
Learn and understand why these are all VERY differnet IPs: 192.168.1.1, 255.255.255.0, 127.0.0.1, 10.0.0.1, 8.8.8.8.
Try to understand subnets and CIDR notation.  What’s the difference between a /32 network and a /24, etc.
Lastly, and probably most importantly is to learn and be extremely comfortable using linux. the highest end routers are mostly configured using cisco command nomenclature on some form of         linux hardware. Use the command line as much as possible!

Ultimately there are as many ways to learn about networking as there are people who use networks. Follow your interest and never be afraid to ask why or how.