Sign in to your PayPal account and click on Merchant Services.
Fill in all the information for your product you want to sell.
Copy your button code
Then edit or add a new page with the content editor and click on (Source) and insert code at the bottom of the page of html codes if there was content there first. If not it would be a black page and you can add the description after you add the button codes.
Now click on Source again and you will see the PayPal button. Now add the rest of the page content in the Visual Mode like you would normally using the WORD like editor. Save when done.