I assume one condition is sufficient? Then something like this should do it:
Assuming that in all cases the salary must be greater than @param1 and @param2 is optional. Also assuming that you pass the parameters as varchars, something like this might do it.
select * from Employee
where Salaries > @Param1
and (coalesce(@Param2, '') <> '' and Salaries < @Param2))
or (coalesce(@Parame, '') = '')