Login into your jomla website, go to content where you see all the articles/pages you created or posted, then click on any of them where you put the products/service you want to sale, when it opens, on the editor box you will see HTML icon, click on it, when it opens paste the html code at the button of the whole code and click save and also save the edit. Review your site you will see the "Buy" or "Price"or "checkout" button etc