Start with tiny obstacles. Always use the same command. Give plenty of praise and encouragement.
You could try throwing tasty titbits over the obstacle if it's a reluctant jumper.
Walk away from your dog, providing the obstacle is not too big, the dog will be desparate to follow and should jump to get to you.
Don't overface it by expecting it to jump pig netting topped with barbed wire immediately.. Work up to that only when the dog is jumping consistently and easily clearing the top of the obstacle.
Give your dog lots of different jumps. You might find a dog will jump a five bar gate but