Need some help getting started

[Sunking]

I doesn't tell "ALL". But it is a good starting point.
I didn't see anything explaining why the C/12 charge current. Or why you use a C/8 for FLA batteries.

That would be a set of encyclopedias. But to answer your question it has to do with internal resistance, stratification, and gassing voltages.

[PNjunction]

If you charge a stationary FLA with less than C/12 current, you encounter acid-stratification in the electrolyte over time. Meeting this minimum C/12 rate will help assure that slight charging bubbles will help keep the electrolyte from doing that. Stratification is bad. In a vehicle, it normally sloshes the fla electrolyte around so stratification isn't a major issue. Think oil and vinegar salad dressing left to sit around.

C/8 is a maximum charge current limit typical for fla batteries that is a general guideline if the manufacturer itself doesn't specify differently, ie if you have a 100ah fla battery (rated by the manufacturer at their 20-hour rate typically), then you wouldn't want to hit that battery up with more than 12.5 amps of current continuously.

Contrast this to AGM batteries where the maximum initial inrush current might be represented as 0.25C or C/4 for example.