if you want adsense within posts use any adsense plugin like All in one Adsense and YPN or look here: http://www.webdesign2day.com/2010/10/31/wordpress-adsense-plugins.html To add ad units on side bar place a new text widget and inside that widget copy paste your adsense code.
Adsense and YPN steals your money, I heard. Use "Quick Adsense" plugin. I heard they DON"T steal your money.
I'm using Quick Adsense plugins for the last few months, it also allows you to use not only Adsense but also other ad programmes, You just need to generate the ad code and then give the code to this plugin, set your location and you are done.