well u should try to catch falling furniture while trying to get on this yellow thingumabob and go near her then she gets captured and you WIN yay

A gizmo is simply a device for which the speaker either does not know or has forgotten the actual name. It is impossible to determine what function a gizmo has unless we know what specific device is actually being referred to. Other terms that are commonly used in this way include "thingumabob", "thingumyjig", "doohickey" and "whatchamacallit".