fan hyn is used when we want to refer to a particular spot. It is often used in a more emphatic way than 'yma' - 'right here' (where I am indicating), or 'here' (not over there).
There are several related expressions for here, there, over there, etc, but this one is a common one.
(fan comes from man (place or spot) and hyn is 'this', so the mutated fan hyn - 'on this spot' which is usually phrased in English as 'here' or 'just here'. The mutation is because of its use as an adverb of place.)