Fortunately, once you learn what the terms mean, it's easy to comprehend how they work. The key difference is the geographical areas they serve.
Local Area Network (LAN)LAN stands for local area network. It covers, as the name suggests, a local area. This usually includes a local office and they're also pretty common in homes now, thanks to the spread of Wi-Fi.
Whether wired or wireless, nearly all modern LANs are based on Ethernet. That wasn't the case in the 80s and 90s, where a number of standards, including NetBEUI, IPX and token ring and AppleTalk. Thanks in large part to its open technology, Ethernet rules supreme. It's been around since the early 70s and isn't going away anytime soon.
There are two ways to implement Ethernet: twisted-pair cables or wireless. Twisted pair cables plug into switches using RJ-45 connectors, similar to phone jacks. (Remember those?). Cables plug into switches, which can be connected to other networks. A connection to another network is a gateway that goes to another LAN or the Internet.
The other popular Ethernet access method is over Wi-Fi under the IEEE 802.11 standard. Almost all new routers can use the b/g/n standards. IEEE 802.11b and g operate in the 2.4 Ghz spectrum, while n operates in 2.4 and 5 Ghz, allowing for less interference and, thus, better performance. The downsides to wireless are the potential for interference and potential eavesdropping.
Wide Area Network (WAN)WAN, in contrast to a LAN, refers to a wide area network. The name is exactly what it sounds like: a network that covers an area wider than a LAN. Beyond that, the definition is less clear. Distances can range from a network connecting multiple buildings on a corporate or college campus to satellite links connecting offices in different countries. The most popular WAN is the one you're using to read this article: the Internet. It's actually a collection of other networks, including other LANs and WANs - hence, the name.
WANs can be wired, using fiber-optic cable, for example, or wireless. A wireless WAN might use microwave or infrared (IR) transmission technology, or even satellite. Laying fiber may make sense when connecting a campus but becomes more expensive when connecting greater distances. To save money, an organization may opt for wireless technology or lease lines from a third party.
Virtual Private Network (VPN)Another method that has become popular in recent years is the use of a virtual private network, or VPN. It uses the Internet to allow people to log into a network remotely and access its resources, but encrypts the connection to thwart eavesdroppers. If your company sets you up with a VPN, you can access your corporate intranet, file servers or email from home or a coffee shop - just as if you were using it in your office. This makes VPN a popular way to support remote workers, especially in fields where privacy is paramount, such as healthcare. Windows, Mac OS X and many Linux distributions can act as VPN clients right out of the box.
Remote desktop virtualization takes this process even further. The entire desktop and applications run on a remote server, and are accessed from a client, which can run on a conventional laptop or even on mobile devices such as tablets or smartphones. This makes virtual desktops great for supporting BYOD (bring your own device) schemes. If a device is lost or stolen, the data is safe because it lives on a central server. Citrix and VMware are the biggest known vendors of virtual desktops.
Personal Area Network (PAN)PAN stands for personal area network, and again, it's exactly what it sounds like: a network covering a very small area, usually a small room. The best known wireless PAN network technology is Bluetooth, and the most popular wired PAN is USB. You might not think of your wireless headset, your printer or your smartphones as components in a network, but they are definitely talking with each other. Many peripheral devices are actually computers in their own right. Wi-Fi also serves as a PAN technology, since Wi-Fi is also used over a small area.
Metropolitan Area Network (MAN)A metropolitan area network (MAN) (not to be confused with "manpages" in the Unix and Linux world) connects nodes located in the same metro area. For example, a company located in the San Francisco Bay Area might have its buildings in San Francisco, Oakland and San Jose linked together via a network.
One of the most common ways for organizations to build this kind of network is to use microwave transmission technology. You might have seen a microwave antenna on a TV news van, extended high in the air, beaming video and sound back to the main TV studio. It's also possible to wire buildings together using fiber-optic cable, but as with WANs, most organizations that use wires will lease them from another carrier. Laying cable themselves is quite expensive.
In the past, organizations that had a MAN used asynchronous transfer mode (ATM), FDDI or SMDS networks.
As you can see, although these types of networks may sound confusing, once you learn the meaning behind the acronyms, you'll find that the concepts are really self-explanatory.