I'll start with the cordless drill/driver, probably the most common variant of the drill these days.
|Author: Luigi Zanasi|
Next, the corded drill.
The two above types of drill are often available as hammer drills. This adds a specialized clutch that can be set to produce a hammering action, for masonry drilling. This adds weight to the drill, but can be very useful for infrequent light masonry drilling, . If you need to do a lot of masonry drilling, buy a rotary hammer instead. A hammer drill takes a ridiculous amount of time to drill any type of masonry other than mortar joints.
Moving on, we have the impact driver.
This tool, rather than a normal chuck, is designed to accept only screwdriver heads. It turns the head by means of a hammering action, which also prevents slippage. It's also much lighter. It's main disadvantage is that it does not provide precise torque control, so care must be taken not to overdrive screws.
In my opinion, these are the three most important drill like things to be aware of.