A pastry blender does exactly what it says. Use it to cut butter or shortening into the dry ingredients for pie crusts, biscuits, and other baked goods. I also use mine for other tasks, like chopping the eggs in a bowl for Egg Salad.
You can probably find one at a discount store in the five dollar range.
If you need an alternative to a pastry blender try using two dinner knives in a criss-cross motion.