We often come across people at airports, libraries, restaurants, etc. using electronic devices such as notebooks, to access the internet without using cables for the connection.
The so-called Wi-Fi network is a wireless network (also called a wireless) where we can access the internet only by radio wave signal, as well as televisions and cell phones, and it is not necessary to use connecting wires.
Radio waves are electromagnetic waves (formed by the combination of electric and magnetic fields that propagate in space perpendicularly carrying energy) used by radio broadcasters.
Basically, where there are systems that make use of radio waves, an electrical circuit is responsible for causing the oscillation of electrons in the transmitting antenna. These electrons are accelerated and, as a result, emit radio waves, which carry the information to a receiving antenna.
Wi-Fi networks, used to provide wireless internet access, operate in the same way: a (wireless) computer adapter captures the information and translates it into radio signals, which are transmitted with the aid of a antenna.
The router (also wireless), whose function is to perform the distribution of network signals, as well as "choosing" the best way to send a data set, is the one who receives the signal and decodes it. It is he who sends the information to the internet using a (wired) connection, the Ethernet, responsible for interconnecting local networks.
It is worth noting that the reverse process can also occur: the router can receive information from the internet, translate it into radio signals and send it to the adapter.