I also want to know that, if I place my add with google adwords, some clicks occure on them, but unfortunately no purchase occures then will google charge me the money for those clicks? and how will it do so.?

If you have a good site with at least 100 pages and plenty of visitors, you can earn a few dollars fairly easily with Adsense – maybe up to $100 in a month, or a bit more. There are a few people earning thousands, but not many – and they have huge sites with hundreds of thousands of visitors.

There's no point using Adwords unless you're also selling something on your site. You have to pay out for every click that's made on your ad, and obviously you'll pay out more than you're likely to earn, unless you have a very popular site already. And if it's popular already, there's no real reason to use Adwords! Adwords is good if your site is selling a product, or service.