Teaching a weanling to tie safely is a critical life skill — a horse that pulls back against a tie rope can injure its poll, neck, and legs, damage facilities, and create a dangerous learned behavior that becomes increasingly difficult to correct as the horse grows stronger. Teaching tying correctly from the beginning, before the horse has the strength to make pulling back a viable escape strategy, is far easier than correcting it later.
The foundation of safe tying is teaching the foal to give to pressure on the halter — moving forward and releasing tension on the lead whenever it feels rope pressure — before any tying is attempted. This is the same concept as leading: forward movement releases pressure. A foal that has thoroughly learned this concept in-hand will transfer it to the tie situation much more readily than one that hasn't.
When tying for the first time, use a strong safe tie point at approximately wither height — never tie lower, as this makes it easier for the horse to generate the leverage needed for a hard pull-back. Tie with a quick-release knot that can be freed instantly if the foal panics badly, and tie with enough length of rope that the foal can lower its head naturally but short enough that it cannot get a leg over the rope.
Stay nearby for the first tying sessions to reward any relaxation and to release the knot if the foal genuinely panics before it has learned to yield. Gradually extend the duration and distance over many sessions. A foal that has learned to stand tied calmly for thirty minutes while being groomed or while the handler does other tasks nearby is fully broke to tie and safe to leave at a hitch rail or wash rack.