What I did: I was participating in a Scouts Drone workshop.
What I learnt: I learnt that the majority of Drones are quadcopters, which are flying vehicles that have four rotors which spin in the opposite direction from the one that is across from it. What this does is that it cancels out the rotational force from the rotor across from it, thus creating lift. The rotors at the rear allow the Drone to move forward or backwards depending on how much power is put into those rotors, the concept is the same for moving in other directions. But, the more rotors a craft has, the more aerodynamically stable it is and it can also bear more weight.
Summary: Rotors help a craft fly and control its flight path.