Both Eriray and Kevin have told you how to physically inhibit the horse from rearing. There are other more drastic methods.
But a horse which has learned to rear at such a young age may well come to represent a serious problem as it gets older and bigger. It must be stopped but hopefully without learning any more unacceptable evasions. Rearing is not the only evasion open to horses: they can shy,kick, bite, buck, balk, whirl and bolt.
But what are you doing to this horse when it decides to rear?
It is one year old, how did you wean it?
How long have you had it?
What are you in the short term aiming to do with it?
What breed is it?
Horses have clocks in their heads - they know the time of day but they can't count. They don't have calendars or birthday parties. It is the human who has this concept of a schedule. A horse just has daytime and night time. Some horses just take their time.
If a horse rears, then for sure he doesn't want to do it.
So then you have a choice, either wait till tomorrow or force him.
Me, I'd wait till tomorrow, I would not want a horse that reared everytime he did not want to do something. So there has to be another way.
My guess, if you must train a yearling beyond simple handling, then quit doing the things it doesn't like and do the things it does. You have plenty of time.
Oh, and as for not understanding what you ask for - that is definitely not the horse's fault - that is yours. You are obviously speaking the wrong language. Try sign language - use your hands.
Tom Dorrance says, amongst other things, that the best way to train a horse - is to get the horse to think it is a good idea. The advice doesn't solve the problem but it gives a clue to the solution.
Starr, time is a great healer. Take it.