Waze highlights the lane you should be in for upcoming turns. It also tells you when to keep straight.
How it works
As you approach an intersection or highway exit, all lanes on the road appear at the top of the map. Waze highlights the lane you should be in to perform your next turn.
Also, Waze will tell you when to keep straight in complicated areas (so you don't accidentally exit a highway, for example).
Lanes are only shown when approaching complicated junctions. If you don't see lanes at the top of your map, it might be because there aren't many options on that road.
If you think lanes should be added to a certain area, you can suggest an edit to the map.