This is the detailed version of what happened. Please have a little patience and read this. I think my problem is unique.
Initially I had installed Eclipse and followed all procedures and was happily coding my first app. One fine day I fired up the SDK manager and saw the Android Tools had a new update. I tried to install the package. Then may be due to my slow net, something went wrong and Eclipse didn't work at all. It said there was something wrong in some file as an error message.
So I installed Eclipse again and followed all procedures. The address of the workspace and the Android SDK was kept same so that my projects will be automatically imported. But now Eclipse is underlining the R or Resource references in my src files. I do not know what to do.