Technically you're off a bit with some other parts but i'll leave it.
So the end bit - People opted out of serps and swapped a guaranteed income (paid by the state) for investment risk via their own personal arrangement, with zero guarantee.
To understand this subject, you need to know the differences between COMP, CIMP, defined benefit schemes and the interaction with historical features like the pre 1997 GMP and its deferment and escalation requirements.
I can tell you now, unless you did this in some professional capacity, you will never fully understand it. Not even close.