Adding Adsense

I am using the theme Live by Herdo in which I saw another site had put Adsense in the sidebar as well as across the top. Do I add the adsense through the text widget by adding the widget to the sidebar then putting the adsense code there? Also, how would I add it to the top of the page? I’m not sure if this is the best way or if I am supposed to get a plugin… Thanks for any help.