If you wish to use either the platforms or zipline, you must first activate the power. After that, you must unlock the area that the platform or zipline ends at, otherwise it will not bring you anywhere. The zipline can be used if there is no notice saying "Closed set" (indicating that you must unlock it) or "Power must be on" (power needs to be turned on). Once the zipline is active, jump into it near the edge and you will use it. The springing platform can be used once the area (lighthouse base) is open, and the power is on. When you stand on it, you will hear a compression sound, and after a moment it will launch you away. Beware, zombies and George can also use them.