Each of these buttons have a task. Some may do several tasks depending on what mode your camera is in. The model of your camera will also have an influence on the number and function of these buttons. It seems the more expensive the camera the more buttons it has.
Regardless of the cost or size of your dSLR the first step to discovering what each of these buttons do is your instruction manual. As you go through this article you might want to have your manual opened next to you. As we go down the list you can reference your manual and compare your camera's function with what is discussed here.
This illustration shows some of the most commonly encountered buttons on a digital SLR. As you can see, they are divided into four groups with a variety of buttons in each group. Let's go over them one at a time starting with the shutter button.
Shutter release button: This is the one button most people are completely comfortable with as it has a very simple function, taking a picture. However, that's not all it does.
By pressing this button half way the camera does two things simultaneously; activate the auto focus (if it's on) and activate the camera's on-board reflected light meter. So in one step the camera is focusing the subject and taking a light reading.
If you are in manual mode you will use the meter to set your camera's exposure setting. If you are in one of the auto modes the camera will do this adjustment for you and you can simply press the button the rest of the way and take the picture.
Mode dial: This dial allows you to select the operating mode your camera will be operating in. For beginners the first mode they'll explore is the 'P' program mode. In this mode the camera handles both aperture opening and shutter speed. The user will have to manually dial in the ISO rating.
Advanced users will work with the 'M' manual mode. With this mode the camera operator makes all the selections regarding exposure; ISO, shutter speed and aperture opening.
Two other commonly used settings are the 'A' or 'Av' mode for aperture priority and the 'S' or 'Tv' mode for shutter speed (time value). Different manufacturers will use different markings but those are the two most common ones.
Depending on the camera, there will be other additional selections. These include user programmable settings and scene specific settings such as sports, close up or night.
Function buttons: These are numerous and have a variety of functions depending on the model. Most models do share some basics and are seldom manufacturer specific, meaning there is a uniformity across makes and models. They include;
Menu and Info buttons. These allow the user to access the camera's menu system and image information respectively. The menu button allows access to seldom used functions such as mirror lock up, multiple or double exposures, flash functions such as sync speeds, rear curtain/second shutter firing, etc. You can also access things like battery info and memory card formatting.
The info button is usually tied into accessing information about an image or information about the current camera settings. This includes accessing histograms and the various user controllable settings such as shutter speed, aperture and ISO as well as white balance and timed shutter release.
The plus and minus buttons are usually tied to the preview button. They allow you to preview, or 'chimp', the photos you've taken. You can zoom in or out with the (+) and (-) buttons. If your camera has live preview mode (the rear display rather than the viewfinder) they allow you to zoom in to check focus.
The [-/+] is used for exposure compensation and the star button is used to lock exposure, focus or both (depending on how you set up your camera.) The grid [-+-] button relates to the focal points viewable through the viewfinder. It toggles through the different focusing modes and allows manual selection of the focusing points.
Lastly, the trash button is used to delete images from your camera. You will find the more expensive the camera the more function specific buttons it will have. There may be a button for white balance and a button for the self-timer for example.
Selector dials: Usually found in several locations, selector dials are large wheels or omnidirectional buttons that allow the selection of an item from a list. For example, the aperture/shutter speed is selected by turning a dial up or down from one setting to the next. They are also used to make selections from a list in the camera's menu. On some basic models the selector dial is used in conjunction with a function button and some dexterity is needed to use them.
Display screen: Your camera may have a variety of display screens available that displays the state of a function or setting. The viewfinder has a limited display that is geared toward exposure settings (aperture, shutter speed, ISO) and well as battery life and focus points.
The camera will also have a large display screen on the back of the body that serves multiple uses. It can show you a preview of the image you just took or it can display the image information, including histogram. It can display your current settings from exposure to battery life to white balance and more. It also allows you to browse through the camera's menu to make advanced selections.
Some models may have a smaller display at the top of the body for quick access to camera settings such as exposure, battery and such. Again, the more expensive the camera the more features it will have.
The best way to learn your camera's abilities is to take time and read through the instruction manual that came with your camera. Even if you've had your camera for a while it's good practice to revisit the manual. You will be surprised at some of the hidden functions you'll discover you never knew your camera had.