When is the initial velocity(u) 0 and when is the final velocity(v) 0

well we need some information but here is an example:

A -------------------- B ---------------------------- C
0 10M 15 20M 30

So an object is travelling along with a constant acceleration. It starts from rest at point a and increases in velocity. When it passes a lamp post B it is recorded to have 15ms. it continues to accelerate to C.Distance from a to b is 10 and b to c is 20.

so to find acceleration from a to b.
S = 10
u = 0 (START OF THE JOURNEY)
v = 15 (end of the journey)
a = a
To find acceleration from B to C
S = 20
u = 15 (start of journey is at B)
v = ? (End of journey)
a = a
To find acceleration from a to C
s = 30
u = 0 (from rest at start of journey)
v = ?(end of the journey at c)
a = a

Hope that helps couldnt think of anything

If the initial velocity is 0, and final a positive figure, acceleration (or positive acceleration) has occured.
If the final velocity is 0, deceleration (or negative acceleration) has occured.

just a few more details will help and maybe make it possible to answer this.