Explanation of a formula used to find multiple returns

I am not sure if asking a question about this thread is allowed or if I should start a new thread but it seemed better to ask here.

Originally Posted by NBVC

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Could someone breakdown the above formula and explain it to me? I would like to modify it for my use but I do not understand it. I can understand small parts of it but not the whole formula. I have simplified it using named ranges to get,

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One thing I am confused about is that in the worksheet it is entered in as an array formula (curly braces around the formula) and I do not understand why.