Tyres come in many different compounds and tread depth. they are all basically made the same with a three layered comstruction of a beaded rim which holds the shape and structure of the tyre and hugs the rim when inflated. There is a woven fabric body to the tyre which is woven between the two tyre beads which is then coated with the final layer of the rubber to protect the makeup.
These are then fashioned for the job in hand, road tyres have an easy tread pattern which optimises a good balance and low resistence to the wheel motion. Mountain bike tyres are a lot wider to cope with the terrian they will going over. Tread generally starts at an easy lug length through to very large heavy lugs for the hardest of terrains. Width of a tyre is very important for the type of cycling you do. Generally a road tyre will be 23mm wide and a mountain bike has two widths recognised being 1.8-2.2 inches for cross country riding and 2.1-2.4 for the more robust all mountain or downhill rider.