A lot of skate parks have perfect ledges already setup and reinforced with a sharp metal coping to help you grind. You can also buy rails for your home, or make your own rails. These can work just as well - especially if the height is adjustable. Or, you can make your own "Funbox". A Funbox is a long, low wood box with a metal reinforced edge for grinding. Any of these would be great for learning on. Just make sure that the ledge or rail has plenty of room before and after for you to skate on.
For your first ledge, try one that is about 6 inches to half a foot (15 to 30 cm) off of the ground, but make sure you can at least Ollie that high, since you will be Ollying onto the ledge. Curbs could work very well, but I don't recommend them for learning to 50-50 Grind right at the start. You will want to be able to ride straight at the ledge, and curbs are usually built so this doesn't work well.
Once you have found a good ledge, you can wax it up if you want to. Wax lets you grind smoother and quicker. You can buy special skateboarding wax at your local skate shop. If you are using a local area to learn to grind on, make sure that whoever owns it doesn't mind you waxing the area up and grinding on it.
