The the meter in the camera and the flash work together to illuminate the scene - distance to focus point, bounce, ambient light levels, etc.

For example, when really desperate for a bounce or softer lighting effect & I didn't bring a "modifier", I point the flash straight up and then fold a piece of white paper over the top so that it is tilted 45 degrees over the flash w/ a rubber band. I have even made a "tube" out of heavy aluminum foil to create a spot or "key light" effect when again, truly desperate. There are more permanent solutions than this, but the point is that the camera's meter and flash work together - if you look very closely you see there are actually two flashes - one is a metering flash the other is the "real" flash. - you can use the pop up as a "master" and the 430 as a "slave" off to the side and even turn off the output to the popup so only the 430 would provide light to the exposure - but you will still the popup on the camera flash to meter the scene and "tell" the 430 how much light to emit.

I am just a beginner on the artistic use of a flash - there are several on the forum that are way better. In the manual you can read about 3 channels, and groups of flashes, etc - just points to how - if you really want to chase it - complex it can be made.... or let the camera & flash to the thinking and it should work 99% of the time - A little quick "compensation" if your subjects are close or you don't want to fully illuminate them (there times when you just a little less shadow) all from the Q button menu