Internet Service Provider (ISP) circuit arrives at a modem or Optical Network Terminal (ONT). That hands off to the router/firewall, which does Network Address Translation (NAT (Network Address Translation)), Dynamic Host Configuration Protocol (DHCP (Dynamic Host Configuration Protocol)) and often Wi-Fi in cheap setups. Below it sits a switch that fans out wired ports, and access points that provide wireless. Endpoints — computers, printers, phones, cameras, card readers — hang off the bottom.
Managed versus unmanaged switch matters as soon as a business has cameras, voice or guests. A managed switch supports Virtual Local Area Networks (VLANs), so cameras and guest Wi-Fi cannot see the accounting workstation. A 12-person studio can live without VLANs; a clinic with clinical devices should not.
Wi-Fi is a physical problem pretending to be a software one. Coverage, channel overlap, band steering and client density decide whether it works. Two consumer mesh units in a concrete-walled loft will produce complaints no configuration can fix; correct access-point placement will.
Draw the chain for every client you support, with model numbers, IP (Internet Protocol) addresses, and where each box physically lives. That single diagram is the most-used page of documentation you will ever write.