how to we convert one currency to another is there any formula? or plz give me an example. i have no idea how do we convert.

just use the ratio of the current exchange.

e.g. today:
1 USD = 1.0186 CAD

what is the value of $50 Cnd in US dollars

1/x = 1.0186/50
x = 50/1.0186 = 49.09