New member, New In Ground Pool Owner

Bought a home with a 20x40 concrete in ground pool with liner. 3.5ft shallow end, 12ft deep end. This is a LOT more pool than our previous two above ground 18ft and 21ft x 4ft deep pools, plus we've not maintained a pool in near 10 years. Sadly, the first thing I'll be needing to learn is how to winterize as we don't take possession until Oct. 8th (maybe one quick dip).
Thanks in advance to all those who have already posted info I will search out, and to all those that will answer my future questions.