Internet Service Provider
Let's start with some basics-- just like power or gas, internet must be physically connected to a property and must be turned on. Internet is turned on by the Internet Service Provider (ISP), such as AT&T, Comcast, or Google, who must be paid for this service.
When internet is first set up by an ISP, they will install a cable on the property that connects the property to the internet. This cable is connected to a box provided by the ISP called a modem. In short, a modem translates information from the internet-connected cable into information that your devices can understand and vice-versa.
Router and WiFi Network
The modem is connected by ethernet cable to a router like Samsung SmartThings WiFi. The router creates the named WiFi network, such as "myWiFi-5G", that devices can connect to wirelessly and transmit information back to the router and modem through.
Keep in mind that most modems provided by the ISP have built-in routers that create their own WiFi networks that can interfere with the network created by a separate router.
Internet --> Modem --> Router --> Device