Implement Adsense To My WordPress Blog

Hi,

As I am a new to WordPress, kindly please forgive me if I ask basic questions.

Here is the scenario:
My WordPress blog is http://www.lifewithnokia.com and I want to add Adsense to it. Yes, I already have Adsense account.

I would like to do the following:
– add a Leaderboard-size Adsense Ad below my Header
– add Half-Banner sized Ads in middle of the page

Questions:

1. How do I put my Adsense code into the location where I want on my blog? I would need to know specific instructions.

2. Currently, I am using this Theme: Twenty Eleven 1.3 – can this theme allow me to insert Adsense Ads wherever I want?

Thank you in anticipation.

Rgds,
Andy