Rotation direction switch
Use the sliding switch above the main switch to select whether the tool rotates to the right or left. This gives you the ability to not only drive screws, but to remove them as well.

Universal holder
Screwdriver bits are not usually clamped directly into the drill chuck. Instead, it is common to clamp a universal holder into the chuck and insert the drill bit into this holder. The reason: the screwdriver bits are so short that they can easily drop too far into the drill chuck. 
But the universal holder has another advantage. It is very easy to change drill bits because it is not necessary to keep opening and closing the drill chuck.