I agree, stick the thing in the hotshoe and start snapping. (make sure the batteries are charged up).
One important thing to note, is that the flash (along with the camera) will act differently, depending on which mode you are in. For example, when you have the camera in P mode (when the light levels are low enough), the shutter speed will default to 1/60 and the aperture will go it it's max. These setting probably wouldn't be enough to get an exposure without the flash, but the flash will make up the difference (on a subject that is in front of the camera). In other words, if you are shooting a person in a dim reception hall, the flash will light up the person but the background may show up fairly dark.
Now if you switch from P to Av or Tv, the camera will give you aperture and shutter speed values that will give you enough light for an exposure with the ambient light. Which means that it will likely give you a fairly slow shutter speed. The flash (in E-TTL mode) should give you enough light to to expose the subject. This may give you a better balance of flash exposure and ambient (usually background) exposure. However, you need to be careful about letting the shutter speed get too slow.
When using an on-camera flash, I usually set the camera to manual mode. I set an aperture of the DOF I want and set the shutter speed for the ambient exposure I want. (hint: shutter speed does not affect flash exposure). In E-TTL mode, the flash will match it's power to the aperture (and ISO) that you have set....so even though the camera is in manual mode, the exposure is still fairly automatic. You may need to experiment to find out what shutter speeds will give you what you want, without getting into trouble. Also, you want to watch out for the max sync speed of the camera (probably 1/200 or 1/250). At speeds higher than that, you will need to use the HSS feature/mode (which will limit your working distance and eat up battery power).
The E-TTL exposure is based on a reading from a pre-flash...and as such, is influenced by the reflectivity of the subject. So you may need to adjust it, depending on what is in front of the flash. For this, you adjust the FEC (flash exposure compensation). You can adjust this on the flash, but if your camera has a button/feature for this, it's probably much easier on the camera.