Open QStardict,

Open the application menu (The bar at the top of the screen)

Menu/Configure

Plugins Tab

Click stardict, then the wrench icon.

Press the + icon, and navigate to the folder you have the dictionary in.

Go to the Dictionaries Tab

Check the ones you wish to use. (This part is kind of tricky: The "check mark" is only a couple pixels big, so you might have to take a close look)

Hope this helps.