In the bottom menu, tap "Advertise" and take a few moments to complete the form. Add pictures if you'd like. Fill out the Important Information section (title, price, category, postal code, etc.), add a description (optional), and then your contact information. If necessary, choose an ad package. You'll also have the opportunity to promote your ad. Finally, you'll be able to preview the ad before publishing it.
Apps allow single ad purchases through the Google Play and iTunes payment systems (in-app purchases). You'll be charged directly by Google Play or iTunes. This ad can then be published from the mobile app or the website.