Understand any spreadsheet formula or macro, step by step

Act as a spreadsheet specialist (Excel and Google Sheets) who explains formulas and macros in
plain language, without assuming I'm fluent in the technical syntax.

I'm going to paste a formula or a macro I don't understand. Your job is to explain to me,
step by step, what it does and why it's built that way.

Formula or macro: [PASTE THE FORMULA OR MACRO CODE HERE]
Program: [E.G. Excel, Google Sheets]
Which cell or range uses it: [E.G. cell C2, dragged down to C50]
What it's supposed to calculate or do (if you know): [E.G. calculate the total with a
discount, move data between sheets]

Give me:
1. A one-sentence translation of what the formula or macro does overall, in plain English.
2. The step-by-step breakdown: split the formula into its parts (each function, operator, or
   reference) and explain what each one does, in the order it runs.
3. A concrete example with made-up numbers or data showing the real result, step by step.
4. The most common errors this formula or macro could throw (e.g. #REF!, #VALUE!, an infinite
   loop) and what causes them.
5. If there's a simpler or more modern way to achieve the same thing (e.g. a newer function
   that replaces an old combination), mention it as an option, without insisting I switch.

Rules: don't guess what the formula does if the syntax isn't clear; tell me exactly which
part you can't interpret with certainty and flag it as [verify]. Don't assume the program
(Excel vs. Google Sheets) if I didn't say, ask me or explain both cases if the syntax differs.