Translation of modules I am using Drupal 7.9 and Webform 3.15. I need to translate -select- option on top of list box. Also I have to translate in Captcha module (7.x-1.0-beta2), the text What code is in the image? and Enter the characters shown in the image. How can do this?

How can I translate modules to required language?
You have to switch on the Locale module, which is part of Drupal  core. There you can search for the strings you want to translate.

If you  want to translate an entire module from scratch, I suggest that you read about translation on drupal.org and make yourself familiar with the toolchain. It's fairly straightforward.