These acronyms refer to different wireless encryption protocols that are intended to protect the information you send and receive over a wireless network.
Wireless Security Background
These wireless encryption protocols were created by the Wi-Fi Alliance, an association of over 300 companies in the wireless network industry. The first protocol the Wi-Fi Alliance created was WEP (Wired Equivalent Privacy), introduced in the late 1990s.
WEP, however, had serious security weaknesses and has been superseded by WPA (Wi-Fi Protected Access). Despite being easily hacked, however, WEP connections are still widely in use and may be providing a false sense of security to the many people who are using WEP as the encryption protocol for their wireless networks (either because they haven't changed the default security on their wireless access points/routers or because these devices are older and not capable of WPA or higher security).
Just as WPA replaced WEP, WPA2 has replaced WPA as the most current security protocol. WPA2 implements the latest security standards, including "government-grade" data encryption. Since 2006, all Wi-Fi CERTIFIED products must use WPA2 security.
The bottom line is, if you're looking for a new wireless card or device, make sure it is labeled as Wi-Fi CERTIFIED™ so you know it complies with the latest security standard. For existing connections, make sure your wireless network is using the WPA2 protocol, particularly when transmitting confidential personal or business information.
Wireless Security Implementation
Using WEP/WPA/WPA2 on the client side (e.g., from your laptop or smartphone): When you try to establish a connection to a security-enabled wireless network for the first time, you'll be prompted to enter the security key or passphrase in order to successfully connect to the network; that key or passphrase is the WEP/WPA/WPA2 code. It is provided by the network administrator or service provider.
Using WEP/WPA/WPA2 on the wireless access point or router: Most wireless access points and routers today allow you to select during setup the security protocol to be used. Unfortunately, the default in many wireless devices is WEP--or, worse, nothing. If you are setting up your own network, make sure you use WPA2 or at least WPA.