What is Exposure?

The combination of shutter speed, aperture and ISO is obtained as Exposure

i.e. Shutter speed + aperture + ISO = Exposure.

If you are not using these things then probably you wouldn't need an SLR just go for point-n-shoot cameras.

You can easily understand the working and need of exposure setting through this image:

All the three components are provided with numerical values and one can result in ideal exposure according to the condition by adjusting these values.  

All the three components have their distinct function as shown below:

Now, how, where and when we can use these settings to obtain a good image?

These settings are co-related; always we have to maintain the exposure level by adjusting these values. It depends on what we are shooting and what we need to adjust, for example: If we are shooting something like sports or waterfall or anything in motion then we should play with the shutter speed.

Let see:

We want to freeze the moving object which required 500 shutter speed, which result in low light then we do adjust. The image will result in good light at 125 shutter speed but we want to shoot it at 500 which is two steps higher and causing darkness.

We can maintain the settings by adjusting the two steps:

Aperture f5.6 (1-step brighter)	Aperture f4 (2-step brighter)	Aperture f8 (same)
Shutter 500 (2-step darker)	Shutter 500 (2-step darker)	Shutter 500 (2-step darker)
ISO 800 (1-step brighter)	ISO 400 (same)	ISO 1600 (2-step brighter)

Similarly we can adjust other things too.

Have a good shoot.

What is DSLR?

DSLR stands for Digital Single Lens Reflex

It is called single lens reflex because in this design light travels through a single lens, an internal mirror is used to direct the view from the photographic lens into the viewfinder. When one takes a picture this mirror flips up (cause the clicking sound) and allow the light to hit the sensor. Unlike the compact cameras one can have more prominent view through the view finder because in compact camera the viewing angle of viewfinder and that of a sensor are different which result in the different images i.e.  the image one is going to capture will be different from what we are seeing through the view finder.

Further unlike the compact/point-n-shoot digital cameras SLRs have real time optical view through which more precise and accurate operation can be performed, compact digital cameras have electronic LCD screen through which one can see the digital representation of the view.

The below picture will help you to understand the functionality difference between a compact camera and DSLR camera.

Difference between DSLR and DSLT

Working of DSLRs and DSLTs :

Now its time to conclude that which one is better?

Advantages of DSLTs :

1) High fps (frame per second) shooting.

Flipping mirror which limits the frame rates is replaced by translucent fixed mirror hence can go up to 12 continuous fps shooting.

2) Quality of image.

Flipping mirror goes up and down whenever a picture is taken whenever one takes a picture which causes vibration and result in low quality image. No flipping no vibration hence results in good quality picture.

3) Faster auto focus system.

Focuses moving objects automatically.

4) The electronic viewfinder displays the image continuously, rather than blacking out   momentarily as with DSLRs.

Disadvantages of DSLTs : 

Not good for low light condition because very low light reach to the sensor. 

Poor low light performance.

So, if you are going to shoot in low light then surely it may cause you some problem but the tremendous fps will give you awesome 12 pictures per second.

And what about SLRs, the only difference between these two are of reflex and translucent and one can easily decide according to what they need.