The clue is in the name, jumps are a big part of rabbit jumping. You can buy rabbit jumps; The Dee Millen online store sells a small selection of 'Karlie' bunny sports jumps in the UK. There are also professional jump makers in Sweden, Libra Artic is a popular one and you can have jumps shipped over.
Whether you're making or buying a jump, the bars must be able to fall easily from both directions if the rabbit hits them, otherwise the rabbit could end up hurting itself and losing confidence. The bars can be made of plastic piping, wooden dowel, or even garden canes. You'll probably have noticed many of the jumps are brightly painted too, this isn't just to make them look nice, but it also makes them easier to see. For bar holders, large metal staples are often used, bent with pliers in the middle so plastic piping sits in nicely. Small wooden blocks are commonly used with wooden dowel. Make sure there isn't a large gap in between bars, otherwise the rabbit likely to go through the jump rather than over.
If you can't or don't want to buy or make jumps, you can use simple household items instead. Garden canes could be used as bars, placed on top of plant pots or a stack of books for example.
The most important thing is that the jump is safe. Don't let a rabbit near one until you have made sure there is nothing sharp sticking out and nothing it could hurt itself on.