First of all you need to upload the png or jpeg files that you would like to use as patterns, to the patterns directory or to your desired directory. The plugin needs to know where you patterns are stored. Therefore you have to pass all URLs of the patterns in the patterns option in the plugin call:  

new FancyProductDesigner($('#fpd'), {
 patterns: ["patterns/pattern1.png", "patterns/pattern2.jpg"]
});

To enable patterns on initial text elements, you need to set patternable to true. For text elements that are added via the sidebar, you have to set patternable to true in the plugin options for customTextParameters:  

new FancyProductDesigner($('#fpd'), {
 patterns: ["patterns/pattern1.png", "patterns/pattern2.jpg"],
 customTextParameters : {patternable: true}
});