If you have the glitter sheets, you can use it by clipping the sheet to a shape or element. For example, if you have a png file of a swirl open, you can open a glitter sheet, drag it onto the swirl (it'll become a layer on top of the swirl layer), then clip the glitter sheet to the swirl by holding down the Alt key (PC) or Option key (Mac) while you click on the line between the layer names in the Layers panel. If it's to your satisfaction you can then merge the two layers and you're good to go.
If you have a glitter style, you just load that into PSE, then apply it to the layer in question to have it completely cover the non-transparent pixels in that layer. Knowing how to load the styles into PSE is another question, which is partially answered in this thread.
and this one