Step 1 :Given the function $f(x)=-3 \sin \left(x-\frac{\pi}{4}\right)$, we can compare it to the general form of a sine function, which is $f(x) = A \sin(Bx + C)$.
Step 2 :In this case, we have $A = -3$ and $B = 1$.
Step 3 :The amplitude is the absolute value of $A$, so the amplitude is $A=|(-3)|=3$.
Step 4 :The period is $\frac{2\pi}{|B|}$, so the period is $P=\frac{2\pi}{|1|}=2\pi$.
Step 5 :\(\boxed{\text{Amplitude: } A=3, \text{ Period: } P=2\pi}\)