Question

when and where the diffferent valency of maganese used

Answer 1

Mostly maganese possess +4 or +7 valency ...It depends on the element which is attached to it
for ex...In Mno2 valency of Mn is +4
In KMnO4 Mn has +7 valency...

Answer 2

The earliest way to find the valency of any element is to know that in which group it is present.