Not necessarily in this order:
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Learn the OSI and TCP/IP layer models.
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Learn the fundamentals of IPv4 and IPv6. (Absolutely learn to count bits for IPv4)
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Learn and understand the use-cases for routers, switches, and firewalls.
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Learn about DNS. (Domain Name System)
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Learn about DHCP. (Dynamic Host Configuration Protocol)
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Learn important Port Numbers for important Services. (SSH is Port 22, for example. The range of port numbers from 1024 to 49151 are "registered ports" that are generally always the same)
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Learn about address classes. (A, B, C are the main ones)
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Learn about hardware addresses (MAC address) and how to use ARP to find them.
And more! This is just off the top of my head. Until you've studied a lot more, please, for your own sake, don't open your selfhosted ervices to the wider internet and just keep them local.
And just for fun, a poem:
The inventor of the spanning tree protocol, Radia Perlman, wrote a poem to describe how it works. When reading the poem it helps to know that in math terms, a network can be represented as a type of graph called a mesh, and that the goal of the spanning tree protocol is to turn any given network mesh into a tree structure with no loops that spans the entire set of network segments.
I think that I shall never see
A graph more lovely than a tree.
A tree whose crucial property
Is loop-free connectivity.
A tree that must be sure to span
So packets can reach every LAN.
First, the root must be selected.
By ID, it is elected.
Least cost paths from root are traced.
In the tree, these paths are placed.
A mesh is made by folks like me,
Then bridges find a spanning tree.
— Radia Perlman Algorhyme