If you are indoors then better bounce the flash off a ceiling instead of using it directly, as long as the ceiling is not too high or colored in a strong color. You can also use the bounce card to bounce some light forward. Some people like to add diffusers to the flash such as the sto-fen and similar.
I recommend using manual mode with flash because in manual you have the control of the shutter speed. Remember you cannot go beyond 1/180 seconds unless you use HSS mode.
Now for fill flash, try this. put the flash on the camera, but dont turn it on. go to av mode and set your aperture, notice the shutter speed, especially if its indoors and the shutter speed is long, now turn on the flash and watch the shutter speed change, thats not good because now its not fill flash, its dominating flash and the ambient is being toned down.
To have it not change, set the flash to HSS mode via the selector on the flash, go to M mode, select the same aperture, and press the green button, it should give you the same shutterspeed you had in Av mode (assuming the ISO is the same, note that auto iso does not work in M mode, make sure its the same) but with the flash on. So now you will take the picture with the same settings as you would without flash, but the flash will fire at a reduced level and fill in some foreground shadow. Note if you dont use HSS sync the shutter speed will still change. If you dont want to use HSS then one trick I have done is to turn the flash off, use the green buton to set shutter, and then turn the flash back on, because its manual the shutterspeed will not change unless you press the green button so it will stay the same.
Consider using manual flash
it may sound difficult but experiemnt a bit with it, there are some very powerfull things you can do with the manual flash, for instance: once you have set the flash power to light your subject correctly, say a person standing in front of some background, and the shutterspeed is set so the background is as bright as the person, now if you want the background darker, then just change the shutterspeed so its faster, the background will be darker but the foreground will stay the same, very powerfull technique.
More notes: BEWARE: if you are using fill flash indoors then that means part of the lighting, usually foreground, will come from the flash, and part of it, usually background, will be the ambient light, now if the ambient light is tungsten lights then you will have a problem. your flash is daylight balanced and so if you set the WB in your camera to flash or daylight then the foreground will look right but the tungsten lit background will have a color cast. In order to fix this you can put correction filters on your flash, these will color the light from your flash so that it matches the color of the ambient light and your WB will look the same.
Quite a lot of stuff there I know, but flash is a very important tool once you learn to use it. flash is also one of those things that if you dont now how to use it and just leave it in auto pointing straight forward, wil make your shots look terrible.
strobist is an excellent suggestion. it does deal with off camera flash, but mentions a lot of things that are relevant also if the flash is on the camera.
Let me link you to some relevant strobist articles:
Color correcting flash:
Strobist: Lighting 101: Using Gels to Correct Light
Balancing flash and ambient indoors, take note of the comparison pictures, this is using manual flash so the flash is consistent and then you can use the shutter to adjust the background:
Strobist: Lighting 102: 3.3 - Balancing Flash/Ambient Indoors
more on balancing flash and ambient:
Strobist: Lighting 101: Balancing Flash and Ambient, Pt 1 Strobist: Lighting 101:Balancing Flash With Ambient, Pt 2
good luck, play around with this a lot and experiment, post pictures and questions of you have them