You've asked quite a few questions, each that is not necessarily as straight forward to answer, but I'll do my best.
For reference, check out this link for some definitions for key terms often used in photography.
[What are the] basics of photography?
The very basics are:
- Adjusting your camera settings
- Aiming your camera at something
- Pressing the shutter release button
And that results in an image, which you then do something with (edit, upload, print, etc).
Producing better images is usually a function of adding more detail to each of these steps.
There are three key settings to photography:
- Shutter Speed
- ISO Speed
Each of these settings are methods to adjust the amount of light that is captured by the camera. In addition to controlling the amount of light, each has a "secondary" function.
Aperture also controls the depth of field--the distance in front of and behind the focal point that is also in focus. A "shallow" depth of field means that the space that is in focus is narrow.
Shutter Speed controls the "stopping of action." Long shutter speeds will blur motion, while short shutter speeds will freeze it.
ISO Speed, specifically when talking digital, increases image noise. This is usually not desirable.
In addition to these settings, camera's have a bevvy of other options, such as autofocus controls, flash controls, metering modes and so on, but Aperture, Shutter Speed, and ISO settings are what is most important.
Aiming your camera
This part, is in my opinion, one of the most vital parts of photography. From choosing your subject, to properly lighting the scene, to setting a good composition, this is likely where you will spend most of your time learning.
As this area is very broad, I can only hope to point you to some decent web sites to better explain this topic.
Pressing the Button
This is probably the easiest step. There are some techniques that you will learn for this, but in most cases, this step is fail-safe.
Buying a Digital Camera
Buying a camera can be a difficult process. I highly recommend buying either a Nikon body, or a Canon body. There are other manufacturers that produce very nice dSLR's, but Canon and Nikon are the two top manufacturers, and are likely to continue to be around for a long time.
I also recommend buying a camera kit, which usually comes with a body and a lens. The typical kit lens is often mediocre, but until you know what you want to shoot, it will be nearly impossible, and cost prohibitive to purchase any other lenses. Nikon and Canon both have models that are suited for beginners, along with mid-level, and professional-grade bodies. All models, regardless of target demographic, will produce excellent images--there are "professional" photographers who make a living through photography who shoot with so called "beginner" models. I suggest you look at these entry-level DSLR (Canon Rebel class or Nikon D40/D3000 class bodies).
One dirty little secret in the photography world is that camera bodies are probably the least important part for making a beautiful photograph.
DPReview has a good buyers guide, which is definitely worth reading.
Assuming you live in the United States (from the OP's profile you live in India--not sure where to buy from in India), I recommend purchasing camera gear from:
And if you live in the greater Seattle Area:
Do's and Don'ts
Here is my personal list:
- Have fun
- Take lots of images
- Think about what you are shooting, before you shoot it
- Ask more questions on Photo.SE
- Experiment--don't be afraid to try new things
- Learn from others. Good photographers borrow techniques. The great ones steal.
- Do lens testing
- Be a pixel peeper
- Ask "is this lens soft?"
- Worry about buying the "best" gear
- Aim directly at the sun
- Aim at a laser