REAR WING & S-DUCT
Rear Wing
The rear wing is probably more simple than the front wing. It's main job is to provide a lot of downforce onto the rear tyres in order to maximise traction when accelerating (as F1 cars are rear-wheel drive). The rear wing works like any other wing with faster moving low pressure air flowing underneath sucking the high pressure air above downwards. Every team will have a number of rear wings with different downforce levels as although they produce a lot of downforce, they also produce a lot of drag which hampers straight line speed. This is why you see completely different rear wings when an F1 car is at Monza compared with at Monaco; they're almost twice as big at Monaco. There are a few little neat elements that are worth mentioning.
On the Mercedes rear wing pictured, there are slots on the side called louvres. There is also a little cut-out behind the wing itself on the endplates. Without the endplates there would be huge vortices created which would produce a lot of drag (as otherwise straight air starts spinning, therefore slowing it down producing drag on the object creating the vortex).
However, even with the endplates, the air flowing over the wing is high pressure compared to the air outside of the endplates which is low pressure. Therefore, some of the high pressure air can spiral over the top of the endplates to the low pressure air causing wingtip vortices which are also draggy.
Therefore, the louvres allow the high pressure air to mix slightly with the low pressure air outside which reduces the pressure differential, therefore reducing the strength of the wingtip vortices.The cut-out is used because the air coming through the louvres are actually now at a higher pressure than the air inside under the back of the wing which also generates a little vortex. But this vortex is spinning in the opposite direction to the wingtip vortex so it neutralises the overall spin and reduces it's effect. See the CFD simulation showing the affect of louvres and the wingtip vortices.
S-Duct
The S-duct is a channel that directs air from under the nose up to the top surface of the nose. Takes air from the bottom of the nose and channels it either underneath the nose completely or towards a 'letterbox' opening at the top of the nose. This solves two key problems.
One is that the boundary layer of air (the layer closest to the surface of an object which is very slow due to frictional/viscous forces) can build up at the front of the nose causing drag and pressure problems. Allowing it somewhere to escape can relieve this build-up.
Second problem solved is that the slope of the nose can cause some airflow separation at the top of the nose. This is because of the gradient of the nose starts steep and then goes quickly horizontal. The air is going too fast to stick with the nose layer as it quickly changes direction. This is inefficient and draggy. Blowing air across the surface energises the boundary layer and keeps the airflow smooth and attached to the nose as it travels down the body.
Overall the S-Duct is a small aerodynamic effect but it is worth exploiting.