The initial value is the multiplier of the exponential part. It is the value when x=0. Here, it is 3.
The base is what has the exponent. Here, it is (5/4).
The function is defined for all values of x. The domain is "all real numbers", or ℝ.
The function takes on every value greater than zero. The range is 0 < f(x) < ∞. In interval notation, it is (0, ∞).