A distance time graph has distance on the y axis (usually in metres) and time on the x axis (usually in seconds). The gradient of the line (change in y/ change in x) is the speed. If the line is flat then the object is stationary.
on a velocity time graph the velocity-time graph the velocity is on the y axis (usually in m/s) and time is on the x axis (usually in s). If the line is flat then the object is moving at a constant velocity. the gradient of the line is the acceleration. The area under the line is the distance travelled.
Initially the only force is weight as drag is proportional to velocity. So the object accelerates downwards. As it accelerates the velocity so the drag increases as well. meaning there is a smaller resultant force downwards so a smaller acceleration. Until the object reaches a speed where the drag is equal to the weight meaning there is no acceleration, this velocity is know as terminal velocity.
Elastic behaviour is the ability of a material to recover original shape after the force is removed. in a spring this occurs when the force is lower than the elastic limit. loading and unloading force extension curves can be different as long as it returns to its original shape.