Get a pneumatic driver. Chuck a screwdriver bit into it. Done. If you mean from scratch, you first need to build a turbine which will use the air pressure to produce rotary motion, possibly gearing to get an appropriate trade-off of speed vs. torque, and a control valve which will let you adjust how much air is coming through so it has speeds other than completely off and completely on. Then you need to affix a chuck of some sort to the output of the gear train, to hold the screwdriver bit. Build an appropriate framework and outer skin for all of this which will let you use it without the risk of getting clothes, hair, or skin caught up in the moving parts If you told us more about what problem you're trying to solve, we might be able to give you more specific advice.