Horses jump naturally - just watch them in the field and if they need to they will jump. Some actually enjoy it and will jump for fun. There are horses which are hard to contain because they will jump 4 foot gates to see what's on the other side!
But you want to jump your horse in a menege and eventually a jump ring so how do you begin?
Start by putting 4 - 6 poles at trotting distance appart. Get your horse to walk over them, allowing him a free rein to look down and sniff them, if he wants to.
When he's happy walking over them, trot him over them, again on a long rein. He may be a bit reluctant at first but drive him with your legs and get him over them.
The next move is a cross pole. Get you horse into a good working trot and be positive - let him have the reins and be prepared for either no lift at all as he may simply trot over as though there's nothing there or prepare yourself for a big pop as he exaggerates the leap. Either is fine, as long as you are positive and don't jab him in the mouth.
The next stage is a straight pole just a foot or so high. Use the same technique as for the cross pole.
A good exercise for jumping and to vary schooling is gymnastic jumping. This is a series of poles, cross poles and srtaight poles to be negotiated in turn. The exercise keeps your horse alert and it's fun, too. This approach will encourage your horse to enjoy jumping.
Good Luck!