Can someone decipher these formulas?

To answer your primary question, yes, we can help decipher those formulas. If you know what any of the individual parts do, you pretty much have it down.

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The two formulas above are essentially the same, except one includes B18 and the other C18.

$B18<>"" means "cell B18 is not equal to blank (an empty string)".
$F18>0 means "cell F18 is greater than 0".
AA$6>$D18 means "cell AA6 is greater than cell D18".
AA$6<=($D18+$F18*($E18-$D18)) means "cell AA6 is less than or equal to the sum of cell D18 plus the product of cell F18 and the difference of cells E18 and D18".

Each of these is a logical test that will return TRUE or FALSE. By wrapping them all within an AND() function, *every* test within the function must return TRUE for the entire function to return TRUE. If any of the individual tests are FALSE, the whole function will return FALSE.

The third formula has an unnecessary second AND() function wrapped around it, and should instead be written as:

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Hopefully that helps!