Where do I start with science subjects?

I have basically forgotten most things about biology and chemistry that I learned in school back then, and I would like to relearn it.

Clicking on the "Science" tab on khan is somewhat overwhelming and I'm unsure where to start.

I'm a college graduate, so am I supposed to start with the AP College biology course because that is "at my age level"? Or am I supposed to start with Middle School, then High School then college because they build on top of each other? It seems like the topics repeat and I'm not sure if they are continuations or they just explain the topics in increasing complexity, so I might as well start with the high level ones if I get the most accurate picture.

But then there is also the "Biology Library" at the bottom with 32 Units. Is this the "complete biology course" that an adult should take?

For me it's kind of confusing and I would love some advice on where to start so I don't end up re-learning the same concepts for hours, only to get the "appropriate course" a while later, which I should have started with in the first place.

Thank you for any advice