The plugin includes a shortcode to show the one-click button, so you can display it wherever you want. This is the shortcode:
And following you find the attributes:
productSet here the product ID that has to be purchased. If no ID is set, it will automatically load the global product, if any.
labelSet here the button text. If no label is set, the plugin will automatically load the default label text that has been set in the General settings as explained here.