Is an impact driver better than a drill for screws?

For driving screws, yes. The impact action adds rotational blows that seat long screws and lag bolts a drill would stall on. A drill is still better for drilling holes and for delicate work where you need control.

What can I drive with a 20 V impact driver?

Wood screws, deck screws, lag bolts and self-tapping screws into wood and light metal. It is not meant for masonry, which needs a hammer drill, or for precision assembly where high torque can strip small screws.

Do I need a brushless version instead?

If you use it most days, yes. Brushless motors run cooler, last longer and give more runtime per charge. For occasional weekend jobs, a brushed model like this does the same work for less.

Does it come with a battery and charger?

That depends on the kit. Many 20 V drivers are sold as bare tools, so check the box contents before buying. Batteries are usually shared across the same brand's 20 V line.