young rider who is new to horses, question about bits. 🎀

hi, i’m a 17yro rider that takes lessons at a local stable, i know the basics about horses and have been riding for a few months now. However, i noticed that our stable never uses bits when it comes to tacking and riding. Does this mean bits are optional, harmful, or unnecessary? I’m not coming at anyone or making claims, i just want to know why most horsey people use bits but we don’t. What is the purpose of them?