In PowerStore, you will need to click on the products update page for the product you want to add powergallery slide show, and then under the long description field, click the source button in the html editor and paste the code that was shown in PowerGallery, and then click the update button.
There is probably needs to be a little bit more of text, but if you have used powerstore admin area, it should have been clear where you need to go to make the update.
let me know if you have any questions.