Voltage current graphs.

[Zishi]

Well, this is really confusing. Sometimes it is Voltage against Current and sometimes it is Current against voltage. This thing really confuses me. Can anyone please explain this whole thing about its gradient, etc? As in velocity time graphs when the curve is going in 'cup' shape, the acceleration is increasing. But in these voltage, current graphs when the shape of curve is like 'cup', the resistance is decreasing. This all is really confusing. A full explanation would be appreciated.