Whatever environment your photographing in, lighting is very important. Whether you're using ambient light (the sun, or overhead lights), or using a flash, it has a very large impact on how appealing your final image is.
When you rely on ambient light, it can create a lot of problems. If it's too sunny outside your shadows will be harsh. If its too dark or cloudy outside you might have to slow down your shutter speed or increase the ISO. Both of which can degrade image quality. You will get the most effective outdoor ambient light either in the shade on a sunny day, during an overcast sky, or taking advantage of the "Golden Hour" Right after sunrise, or right before sunset.
Indoor ambient light can create even bigger issues. Unless you have a fantastic camera that handles dark conditions well, or you have a tripod, most of the time you will need additional lighting. That being said, a great light source is the window on a sunny day.
Nighttime photography will require either a tripod and longer exposures, or additional lighting. And if there is absolutely no ambient light (you're in the middle of the woods, in the middle of nowhere) you won't get anything.
Most of the time you use additional lighting will be indoors or at night, it is rarely used outdoors in the daytime unless the photographer wants a specific lighting look on a subject with an outdoors background.
You have a few options for lighting.
- Your on camera flash-can be weak and create unattractive shadows.
- A hotshoe flash-generally attaches to the top of your camera, more powerful, but unless a diffuser or it is angled to bounce it has the same issue with shadows.
- Strobes-are much more flexible in a studio setting, you can move them, and have more adjustment options.
- Hot lights-stay on all the time, so they get very hot. Not commonly used.
When it comes to lighting there is some equipment that can be helpful.
Light meter-reads light and can give you advice on how to adjust your lighting for a good exposure.
Bounces or reflectors-are reflective surfaces that can help you direct light, usually use for fill light (to "fill in" shadows).
Diffusers-are materials you attach to a light source to soften light, and decrease shadows.
Umbrellas-are used to bounce light onto a subject, although there are "shoot-through" umbrellas that act as diffusers.
Soft boxes-are gigantic diffusers that give optimal lighting for portraits.
Gels-can be played with to create colored lighting, or correct off colored lighting.
Essentially if you're wandering around and need a flash, a hotshoe flash with a diffuser works great. If you're working in a studio, strobes with a soft box are normally best. And if you're outside in the daytime, you don't need anything. Just be conscious of the direction of the sun and the effect it has on your subject, and you can use a reflector to improve the lighting if needed.