If you have a Adsense account then just generate code and place it on your website. If you dont have Adsense account then you need to sign up for one. Add me on Skype: macsolutions389 and ill help you on how to move further with it.
If you don't already have an Adsense account, you will need to apply: https://www.google.com/adsense/
Apply for adsense and when you are approved just creat ads from your adsense account and just place them wherever you want on your website but never more than 3 ads.
Hy,first your website must to be with good content with because your website must to respect politics to google adsense and after you can to make account for adsense.If you want more info tell me. cheers