At some point you will have to tie up your horse. When you first do this just loop the rope through some string so you can check they are happy and used to being tied.
Gradually increase the distance and the time they are left, until you are sure they are happy and not liable to panic.
Make sure the area you are tying him in is safe with no objects he can get caught on. The ground should be level with some grip, tarmac is not ideal as it can be slippery. Other horses should be at least 2 kicking distances away.
Tie onto a piece of string attached to a secure tie ring. I use thinned baler twine. This is so if the horse gets scared he can break free, which is more desirable than a broken neck or injuries caused from slipping or falling while tied. Also, if a horse is really scared and not attached to something that will easily break, they can pull what they are attached to off the wall. They then have a very dangerous object, possibly with nails sticking out dangling between their legs as they run away.
Use a quick release knot, the one demonstrated means the knot, however hard the horse pulls, will not get tangled in the string.
Put the rope through the string or clip making sure the rope is long enough so that the horse can still move around, but short enough so that he cannot get his leg caught over it.
Put your hand on the rope with your little finger nearest the string.
Turn your hand over to form a loop.
Put the remaining rope over the length attached to the horse.
Push the rope remaining through the loop you have made to form another loop.
Pull the loop so the knot tightens.
Put the loose end through the loop so the horse can not easily untie themselves.