If you have a self hosted blog, simply paste the adsense ad into your theme wherever you want it to appear. If you have a free wordpress blog you can't post adsense there.
You can do it by a wordpress plugin. There are many WP plugins for adsense. Try "WP plugins adsense" term in google. you well get correct plugins to add Google adsense for your blog. Good luck.
I have a self hosted blog on a .com domain. So, i will do this by googling. actually i was considering before that something have to pay. thanks for replies
yes, tell us if you are using self hosted blog or wordpress.com. If it is self hosted then there are many plugins to do this...
You can add direct adsense code in sidebar.php if you want it to be appear in sidebar or else you can add it in posts too by adding adsense code in index.php or single.php. Regarding adsense plugins, there are number of available on net. Such as 1,2,3 and many more. DON.