If you want to join AdSense and earn money online then first you need to have a web site or blog your own. You can use a blogspot blog to apply for AdSense. Main thing is your blog or site has to be few months old and should have lot of unique content. otherwise they might reject your site.

There are some types of sites which are not allow for AdSense such as Adult sites, Warez sites, gambling sites etc. Also site need to have a privacy policy and contact page. You need to put lot of unique content for a site you want to apply for AdSense. It might take 1 day to 2 weeks to receive a mail from AdSense telling yr site is accepted or rejected. Few things you need to do before apply for AdSense,

• Read the Google AdSense TOS and check your site comply to it or not.
• Site shouldn't be in not allowed topics of AdSense.
• Your Site need to have a Privacy policy.
• There should be a contact page.
• Don't apply for AdSense unless your site gets at least 50 visitors a day