Someone asked these questions about AdSense, and I though I might as well answer them in a post. Will expand on this post as I have more to add.

1) How can i earn from Google Adsense.
2) How will i be paid for it .
3) Do i need to pay anything to Google for this .
4) If i need to pay anything how much it is .
5) Will my personal information will be kept confidential.
6) Do i need any special software.

How can I earn from Google Adsense

You can earn from Google AdSense in three ways:

Contextual Advertisements
By placing contextual text or images ads on your sites. These ads are of two types - CPC (Cost per Clicks) ads for which you will only be paid if readers click on the ads, and CPM (Cost per 1000 impressions) for which you will be paid for just displaying the ads on your site, irrespective of whether the readers click on them or not. Although it is Cost per 1000 impressions, you don't need to reach 1000 impressions to be paid, but you would be paid proportionately for each click.

AdSense Search
You can put up to 2 AdSense search boxes on your site. They can be just for searching the Web, or they can be used for searching only the content of your site. You will not be paid for readers for using the searchbox, only if they click on any ads that may be displayed in the search result page.

Referrals
You can also earn by referring people to join AdSense or to get AdSense or Google products. You can place referral buttons or text links on your sites, and if your readers click on these, you may be paid under certain conditions. Currently, there are 4 referral products that available - Google AdSense, Google AdWords, FireFox with Google toolbar and Picasa. For Google AdSense, if your reader join AdSense via your referral button, you will be paid US100 if they manage to earn US$100 within 180 days (6 months). For Google AdWords, if your reader sign up and spend US$100 within 90 days, you will earn US$20. For FireFox with Google toolbar, if your reader download, install and runs the browser for the first time, you will be paid up to US$1 depending on their geographical location. For Picasa, when a user you've referred to Picasa downloads and runs the product for the first time, you will earn up to US$1, also depending which geographical location.

How will i be paid for it
You will be paid if in a month you earn US100 or more. If you earn less than that, you will not be paid, but the amount will be carried forward and you will be paid when the total reaches US100 or more. You will normally receive your payment by check sent to the address you registered when you apply (even if you don't live in the US). Some countries have the option of being paid by EFT (Electronic Fund Transfer) where the payment is transfered by wire, and will be faster and cost less than being paid by check.

Do i need to pay anything to Google for this
No, you do not need to pay anything to Google. However, for earnings obtained from ads via AdSense searches, some amount may be deducted for the cost of performing the search, but the amount deducted will never be more than what you earn.

Will my personal information will be kept confidential
The only information that anyone can get from the Web is your AdSense ID (which can be obtained by viewing the source code of pages which have your AdSense ads, but which will be useless to them as far as getting personal information about you.) No other personal information is displayed anywhere on the Web.

Do I need any special software
No, you don't need any software or download anything from AdSense. To participate, all you need to do is to sign into your AdSense account and generate the scripts you need to add to your site to get the AdSense products displayed.