That Vivitar unit is non-dedicated (one reason why it's so much less expensive). That means that there is no communication between camera and flash (except when to fire). I do believe that is has it's own metering sensor though.
In practical terms, it means that you would need to match the settings on both the flash and the camera...and when you change the settings on one, you would need to change the other as well. It's not really hard to do but it's not fool proof and it's not as easy as using a dedicated flash.
With a dedicated flash unit, you put it on the camera and it will match it's output to the settings on the camera, you basically don't have to touch the flash. You can even adjust the FEC (flash exposure compensation) via the camera controls. It's very easy to use and it's pretty much automatic (in E-TTL mode)...but it still allows you to be creative with the camera.
Also, the 430EX has the functionality to be used wirelessly in Canon's wireless system (more about that later).
When using a flash off camera, you need to trigger it somehow. Canon does have a wireless system that requires one 'Master' unit and one or more 'Slave' units. The 430EX can be a slave only. The higher end 580EX can be a Master or a Slave and the ST-E2 is a Master only (it's not even a flash). In this system, the remote flashes still have E-TTL functionality and metering. The major problem with this, is that it's range isn't great and unless you are in a smaller room, you need line of sight between units.
There is also a Canon off-shoe cord, to get the flash off camera with full functionality...but it's not very long...best used for hand held or bracket mounted flash.
Another way to trigger an off-camera flash is with a cord or radio triggers. The cord is pretty straight forward, it' connects to the camera and to the flash. If the camera or the flash do not have the proper connection points, then you would need adapters. Radio triggers are a very popular way to go because a radio signal is very good and doesn't need line of sight.
The disadvantage of a 'PC' cord or radio transmitters are that you can't use E-TTL anymore. It becomes manual flash control and metering. It's not really hard to do, once you understand it...but it's not really child's play either.
You can use either a dedicated or non-dedicated flash for manual off-camera flash. For this reason, many people recommend the non-dedicated units for this type of thing because they are cheaper. A dedicated flash can do both though, which can be a big advantage.