It's basically a power strip:

but specifically for cables that carry Internet traffic instead of electrical power.

A more direct analogy would be a telephone switchboard (which is why it is called a "switch"), basically a computerized version of those old-timey operator ladies who used to sit in a room waiting for you to make a phone call, and they'd physically move a plug connected to your phone and plug it directly into the phone line of whoever you were trying to call. That, but for computers trying to talk to one another over network cables instead of making telephone calls.

A network switch

From my basic understanding (literally just setting up my home Internet) it turns one Ethernet from the router into like 20 different connections for each computer or device

Keep in mind that I literally have no experience and can only give you the Wikipedia but I can't make sense it except for laughing at the word 'GigaSwitch'
https://en.m.wikipedia.org/wiki/Network_switch

Layer 2 switch