Hey Lakshman,
No sweat man, just passing on what I have learned thus far. I'm in the same boat as you, new and learning, there are a bunch of people on this site that have much more experience and knowledge than I.
In terms of what site do I use for looking for units? I think they are all the same, (Redfin, Zillow, Realtor) in term of listings with the only real difference being the user interface.
In terms of what I look for in markets, it is nothing special or unique and I'm sure others have a more comprehensive list than I. Factors such as migration (in/out), median housing and rent price, tax rates, median income levels, rental vacancy rates, etc. This is easy stuff to find and a lot of it can be found on census.gov:
U.S. Census Bureau QuickFacts: United States
Go to that link and plug your desired market in, and you will see a lot of useful information.
Also, all the calculators, guides, and BP Insights found on this site are also pretty valuable. Once you have the big stuff figured out then you will need some "boots on ground" if deciding to invest out of area.
Again, this is just my own newbie stuff here, hope it helps you at least a bit. Looking at the other comments above I can tell there are a lot of other people watching this string that have a lot more knowledge than I.