If you are even slightly knowledgeable about networking, you do not need to read this. If you just want the minimum necessary to connect to a network without understanding what's involved, read only the very few paragraphs in bold.
Networking (connecting computers) can be of two kinds: Wired (connected with cables), and Wireless. Both follow the Client/Server model.
The Client/Service model was invented so one Server can "serve" many clients. While there are dedicated servers and dedicated clients, in general, a device can switch between these roles.
A device central to Networking, is something called a "modem/router" and most modern homes have one of these. The modem/router initialy acts as a server and collects signals from all it's clients. Typically, the clients are computers and cell phones, but in a very modern world, the client list can also include printers, tvs, temperature or lighting regulators, and maybe even cars.
After the modem/router fulfils its server function of collecting all these signals and determining where they need to go, it switches into client mode and transmits the information to servers further down the line. These down-the-line servers can include a giant modem physically located at your ISP, a satellite or large tower launched/built by your cellular provider, or a tiny print-server chip in your network-enabled printer or a fax-server in your network-enabled fax machine.Back to more practical stuff: If you are going to attach to a network through wire, you will need to connect a network cable between your computer and a designated port on your modem/router. Until now, the expression "network cable" has been synonymous with "Ethernet cable", Ethernet being a very early standard for computer devices to communicate. But currently, USB is the most actively advancing protocol, and I'd be very surprized if already or in the near future, you cannot also connect your computer to a modem/router with a USB cable.
Wired communication is relatively secure and only international and domestic security agencies can intercept it, so there are no specific security considerations with wired networking. On the other hand, wireless communication is easily intercepted, so wireless communication involves security procedures and encryption.
Wireless security can be set to any number of different protocols, some of which, in ascending order of protection, are none (unsecured), WEP, WPA and WPA2 Personal, and WPA and WPA2 Enterprise.
In the old days, when I used to vist my daughter and wanted to get Internet on my laptop computer, I would go in the hallway of her apartment and use one of the unsecured networks of her neighbors.
Today, with increasing awareness of wireless security and the perils of ignoring it, it is rare to find an unsecured wireless network. So, to use wireless, we need to know a little about security protocols, which are based upon something akin to username/password protection.
My operating system, Linux Lubuntu, contains a program, GNOME network-manager, which seems to do a pretty good job of knowing which security protocol is being used by nearby wireless networks. Therefore, to connect to a network wirelessly, I need only know the username (called a SSID or ESSID) and the pass-phrase (called a passkey for WEP). Today, towards the end of 2016, most routers broadcast (send out a signal telling your computer) the SSID and you only have to recognize the correct one from all the within-range options and supply the pass-phrase. Some modem/routers are configured to not broadcast the SSID, so you have to know the actual SSID and follow your program's instructions for connecting to a "Hidden" wireless network.
Most ISP-supplied modem/routers come with the default SSID and pass-phrase written on them somehere near the label and serial number. It is possible to change these and if someone did, or bought his/her own modem and configured it, you need to ask this person what the correct SSID and pass-phrase are. Without that information, you shouldn't be able to conect to that network. As discussed above, I don't know if you also may have to ask them what kind of security they are using.