White balance on your camera is there to help make sure that things that appear white in real life also appear white in your images. seems to go in one of two ways. You put on auto white balance and everything looks great. All the whites look white and you don't even have to give it a second thought.
Or...you take a photograph and realise that everything is blue, orange or yellow. Or just plain yucky! This is nearly always because of artificial light that you can't turn off. When I worked as a wedding photographer white balance as some venues was a total nightmare. But these colours can also be caused by low natural light at dusk or dawn.
If my auto white balance isn't working then I try one (or more!) of the following.
First, I check to see if any of the alternative white balance settings on my camera will help. For example Incandescent for domestic lighting.
Second, I shoot in RAW mode. Not all of your cameras will be able to do this but if you can shoot RAW and you are in a tricky lighting situation then I would do it. The files are very large, so you might not want to do this all the time but if you shoot RAW then all the colour data is retained in the file, compared to a JPEG file where unselected colour data (dependent on the White Balance setting you have selected) is not included in the file. This means that when you edit a RAW file you can correct the tone of the white in the image.
I don't shoot all my work in RAW though. The files are too large and apart from for white balance work I rarely use the RAW data, so I just don't feel it's necessary. Pro-photographers are split on this one, so remember this is just my personal view. Other photographers shoot everything in RAW.
Third, I set a custom white balance. I use a grey card to take an image to set the custom white balance to. Each camera you have will have a different button for this. When I do it I take a photograph of the grey card and then go to 'custom white balance' in my menu and select the image I've just taken. The custom white balance will then be adjusted to capture images in the same setting as the one I'm currently in.
Be careful when you set the custom white balance indoors. You must make sure you put it back to Auto White Balance when you go back outside. Otherwise all your images will be really blue!
Have fun! x