Making hard candy isn't really any different from just adding table sugar except that you'll caramelize some of the sugar and change the color/flavor/fermentability a bit. If you want to use the ingredient "Belgian Candi Sugar", you can either spend a lot at the HBS or use bags of white sugar from the grocery store. The real Belgian Candi Sugar is just sugar dissolved in water and then allowed to crystallize on strings hanging in the water.
Invert sugar involves cooking the sugar with citric acid. This breaks the sucrose into simpler sugars that the yeast can ferment much more easily. It will taste cleaner and ferment faster and more easily.
They each have their place in the sceme of things. But it can get confusing.
To make Invert Sugar:
Take as much sucrose as you want (table sugar) and add just enough water to make a thick paste. You'll have to cook all the water off anyway, so the less you add the better. Heat on high stirring constantly. Warning, this stuff can boil over like wort, but it's MUCH messier.
Add about 1/4-1/2 tsp of citric acid (from morebeer.com or beveragepeople.com). Continue to raise the heat until it's at 300 degrees F. Hold it there as long as you'd like. It will darken and generate more unfermentable sugars as it caramelizes. I usually go for the lightest sugar I can.
Then you pour it into your wort. Be careful. It's much hotter than the wort. Stir well so none sticks to the bottom.
Alternately, you can make it ahead of time, heat the sugar to "hard crack" stage and then cool it and keep the "Invert rock candy".
A good time to make the sugar is while you're sparging or while the boil is heating up. Takes me maybe 20 minutes.
Cheers