We assume you already have your Adsense account with Google organized and a ‘Skyscraper’ Google or Amazon (whatever) ad already to paste in.
Open your WPress admin dashboard and navigate to Display(Presentation)/Widgets. You are looking for a widget called Text 1 ( or 2 or whatever is the next free widget.)
If no Text widgets are available in the “Available Widget’ dialog box, scroll down and selct 1 or 2 from the ‘Text Widget’ dialog and when you “save” there will be one or more in the “Available Widget’ dialog. Drag one of these up to the appropriate sidebar box. Click on the little Page Icon, and a dialog will open where you can edit the widget Title and paste in your Google Ad code.