Placing ads on your website using Google Adsense is easy you just need to copy the javascript code that provided by Google and viola ads starting to show up on your website. Related ads with your website content usually show up after a few hours after you put the Adsense code on your website. There is some trick to improve this related ads to be more related to your content.
For example you have a blog with a possibitity for visitors to put comment on your articles, since Adsense shows related ads to your website content there is possibility that the ads being shown is actually more related to the comment’s keywords instead of your original blog post’s keywords.