Smaller horns can be mounted to headbands. However larger horns will need a sturdier base, and are best applied in a manner that they can be removed for storage/travel. (Using screws/bolts in order to attach)
Some can come hollow, whereas most come solid; that is where they are slush cast resin, with a rigid expanding foam inside to help keep them light, but sturdy.
Some are hand sculpted, others are replicas of real horns. They will specify in the description.