When to use coaster brake, and when to use rear rim brake? I have recently moved to Germany (from the UK) and started commuting to work by bike. Apart from the confusion of cycling on the other side of the road, and the levers for the brakes being the other way round to the are in the UK, my new bike is fitted with a coaster brake as well as calliper rim brakes for the front and rear wheels.

I have never ridden a bike with a coaster brake before, as they are unusual in the UK. I am unclear as to when I should use the coaster brake and when I should prefer using the rim brake for the rear wheel? Are they essentially equivalent and I should just use whichever I find easier, or are there circumstances under which I should favour one or the other or even both together?

If it makes a difference my route to work is fairly flat and mostly consists of cycle paths separated from the road, although at this time of year there are a lot of wet leaves on which I'm finding it difficult to control the speed as easily as I'd like. It has been several years since I have ridden a bike.
The coaster brake is the primary brake. It should be used as your first means of stopping. Rim brakes on coaster brake bikes are typically a safety design. If the chain were to break or come off the sprocket you would have no coaster brakes. In the U.S. the hand brake is normally installed on the front wheel. The front wheel provides more braking power as you weight shifts forward.