How to apply to single group/layer?

Any time i ad an object into the project panel for example, a hat. It always applies it to the head of the left and right profile as well. why? and how do i change this? I only want it on the front profile, as i will ad a different hat for the left/right profiles. this is with anything added. you cant simple click the "unsee" button, becuase it makes it unseen on all profiles. Having to do so much workout to make these puppes function is giving me a headache. I hope someone can help its greatly appreciated!