how can i get 6 only using -4 4 times

That is impossible. There is no way to solve this question because we only have -4 to multiply 4 times. And in those 4 times multiplying, the negative number increases. So instead of going to 6, it goes farther back in the negatives.

The question needs better definition.

What mathematical symbols are we allowed to use ?

Can we use moduli signs so that |-4|=4, making the negative sign irrelevant ?

Can we use the square root symbol, so that the square root of the modulus is 2 ?

Can we use the factorial symbol, so that |-4|!=24 ? etc.

since the question doesn't specify, why don't you assume that you can use any symbol.