Also, I am unsure what my teachers mean when they say use randbetween function to find a starting point to work off.
randbetween is essentially an excel function for generating random numbers given two parameters (a lower and an upper bound/limit).
For example, if i wanted to generate a random number between 10 and 20, the function inside my excel cell would look something like:
=RANDBETWEEN(10,20)
It seems like your teacher wants students to have different starting points, given the mention of this function. For example, in your data of 100 months, you could use the randbetween to generate a starting point (this will be different for every student).
=RANDBETWEEN(1,100) will give you a month from Month 1 to Month 100 (as an example, I don't know what your SAC is about or the specific requirements of it, so i'm only giving you advice on this function in general).