I'll tell you. If a function is periodic, i.e., oscillates, it has a period, T such that
f(t+T) = f(t)
The frequency is the number of complete oscillations per unit of time.
For example if T = 1, then there would be one oscillation per unit of time, seconds say. I.e., f = 1.
If T = 2, there would be 1/2 an oscillation per second. I.e., f = 1/2.
If T = 1/2, there would 2 oscillations per second, f = 2.
Given all that, what is the relation between T and f?