A cordless drill spins a drill bit at high speeds. The tip of the drill bit shaves away the material in many small bites.
Drills can be used to drive screws, but will not perform as well as a dedicated impact driver. The continuous torque a drill produces will twist the tool out of the hands of the operator as soon as the screw stars to bind.
Drilling into Concrete: Hammer mode
A hammer gear is required for drilling into concrete, stone, and other porous materials. In this mode the drill adds many thousands of little blows to the drilling motion per second. These blows shatter the aggregate in the concrete when the drill bit encounters it. Without this feature drilling into concrete not only slows down, but can outright stop when the drill bit encounters a stone.
Driving Screws: The Drill/Driver
If you want to use your drill to drive screws, you should consider a drill/driver. These tool slow down the motor and increase its torque, which greatly improves the tool's driving performance. The tradeoff is a slower drill. Drill/Drivers are listed in the Impact Driver section.
1) Choose a type of chuck
The friction chuck is the default choice. It works best for drilling small holes into wood or plastic. This type of chuck makes changing bits fast and easy. Most importantly, drill bits are cheap and available in every hardware store.
The other types of chucks are used for specialty applications. The SDS chuck, for example, secures large, high torque bits. Review the chuck property for more details.
2) Choose a battery voltage
All drills have sufficient power to drive drill bits smaller than 1/2" through any type of wood (some will take longer than others). If you require larger holes, look for a model with a higher battery voltage.
The voltage of the battery limits how much energy is available to the motor at any given time. Higher battery voltage allows the motor to put more energy into the drill bit. Tools with higher voltage generally drill holes faster.
3) Choose a drill with a hammer mode
If you plan on drilling concrete, a model with hammer mode is required.
4) Choose a Battery Interface
Cordless Power tools share their battery with other tools in the same series. Sharing batteries between tools is an economical thing to do. When you purchase your drill consider the other tools in the series. Should you ever need a different tool, it would be best if a tool that matches your drill's battery is on your short list.