Purchases gives you the ability to bring the opportunity to your users to recharge their points, unlock achievements or unlock ranks by an amount of money.
First of all, you need to configure the add-on to setup the currency, taxes, getaways and emails.
You can place a purchase form anywhere, including in-line on any page or post, using:
[gamipress_points_purchase] shortcode to allow purchase points.
[gamipress_achievement_purchase] shortcode to allow purchase access to a desired achievement.
[gamipress_rank_purchase] shortcode to allow purchase access to a desired rank.
Also, you can place a purchase form on any sidebar through widgets provided by this add-on.