While there are several devices that can be used to build a smooth functioning home network, most homes will only require a single "all in one" device usually referred to as a "router". Most electronics stores carry a variety of routers and there are many functions that a router can accomplish besides "routing".
The Multi-Talented "Router"
While it is possible to create a home network or use high speed internet without buying a router, the low cost, ease of use and reliability have made them an essential centerpiece of the networked home. Your router connects directly to your high speed internet modem and to your computer, or other network device. Your router is itself a small computer whose only purpose is to direct traffic. It relays your internet requests out to the internet. It receives data and forwards it on the attached computer. As far as your Internet Provider is concerned, the router - acting like a regular computer - is the only device connected to their system. This in and of itself isn't particularly useful. Of course, most consumer routers can accomplish far more than just routing internet traffic.
Newer consumer routers not only manage traffic from several different devices and relay internet responses back to the source computer, but they allow the connected computers to communicate with each other by playing the role of another network device - the switch. In addition, by following a set of rules governing how incoming internet traffic is handled, the router acts as a firewall. While installing firewall and network security software onto your computer is useful, your router can act as a physical defense against unwanted incoming traffic and help secure the entire network.
Many consumer routers can also play the role of a Proxy, by controlling how the computers connected to it use the Internet. Using your router you can restrict internet access to different computers on a set schedule, restrict certain types of activities, restrict access to specific web sites and record internet activity.
If that isn't enough, most routers also function as wireless access points allowing both wired and wireless connections to the home network.
Even if you don't have a home network, it's important to remember that your high speed internet connection essentially "networks" your computer to the world. With that in mind, an extra level of function, control and defense is nothing short of a necessity.
Be sure to evaluate all options before choosing a High Speed Internet Provider.