The rein is the subtle connection between the rider's hand and the horse. The rein signals can pass back and forth.
Reins are used for work in hand and riding. It is advisable to use reins with a clip on both ends. With these clips you can attach the reins to the rings of the cavesson and change them around easily.
As you become more advanced, you can use a combination of cavesson and bit during work in hand and riding and use two reins.
If you are working with two reins, it is, especially in the beginning, advisable to use different reins for example, a brown one for the cavesson and a black one for the bit. By using different reins you will not get confused and you can easily make the distinction between cavesson rein and bit rein.