You are never allowed to park at bus or tram stops, as parking is prohibited closer than 20 metres before and five metres after the actual stop sign.
However, you are usually allowed to stop to allow a passenger to get in or out of the car – but not to load or unload goods – provided that this can be done safely and without you obstructing the traffic for which the stop is intended.
Note that at some bus and tram stops stopping is prohibited altogether. Where this is the case, the stop is marked with a solid yellow line on the kerb, and possibly also a yellow zigzag line on the street. At these stops you are not allowed to either stop to load or unload goods or to allow a passenger to get in or out of the car.