Drow Ranger had some drastic changes over the last couple of patches. Appearentely Valve didn't like how she worked, so they changed the design but they never were happy with the outcome, chaning her again and again.
In 7.23 Drow had one of the biggest change in her lifetime: They removed the passive global aura on herand moved it to her ultimate. Instead she now has a new skill that fires mutliple arrows in front of her, dealing damage to everyone hit. Interesting change.

So let's take a deeper look at Drow now. Drow Ranger works still the same, you want to build a ton of agility on her because she has a bigger benefit from it than most other heroes. She also works great with other agility based ranged heroes, like Sniper or Luna.
She has a good AoE Silence, a slow attack modifier and her utlimate has a proc chance that deals additional damage and ignores all base armor. This means she is a mean right-clicking hero and her new attack skill gives her now a good wave clear ability and crowd control tool.
Drow Ranger wants to kite foes a lot in fights. She looses the benfit from her ultimate, which means both the bonus attack procs and the aura effect, when enemies come to close, so you have to use your slow and your silence to keep enemies away from you, while retreating between shots. If you keep a safe distance from enemies, you will tear through them.

So in general, you want to build on Drow two types of items: Mobilty items to kite enemies easier and agility items whoich boost your main damage and your agility aura. If you do this correctly and position yourself well, you should be able to make great plays in your matches.