Each plugin's listing generally shows the number of apps a plugin is installed on. Note that this does not necessarily correspond to the number of users who have purchased your plugin, if it is a paid plugin. The number can diverge because of a number of reasons where users have the plugin installed on their app but they are not paying for it, e.g. because they used a template that has the plugin, because they copied an app that has the plugin, because they downgraded their plan, etc. Rest assured though that if your plugin is a paid plugin, a user can only use it if they have paid / are paying for it (i.e. having it installed does not automatically let them use the plugin).