Assistance incrementing a cell that remains based on its current value - Circular Ref.

Hello all, and thank you in advance for your time.

Interested in learning a little about macroing or VBA in regards to allowing one cell to be volatile while incrementing another cell that remains based on its current value.
I've played around with Circular Referencing for this and found its quite messy, prefer to avoid it.

Here is a code i found sifting through forums and trying to learn about the details of SUM and SUMIF:

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Credit for this, with appreciation, to lenze.

Specifically i need to do what this does, from 1 single cell in one sheet to another single cell on another sheet.
So: 'Sheet2' A1 = 'Sheet1' B1
if 'Sheet1' B1 = 2, 'Sheet2' A1 = 2
then if 'Sheet1' B1 = 3, 'Sheet2' A1 = 5
and finally 'Sheet1' B1 = 0, 'Sheet2' A1 = 5

The above code does exactly that from C to D, as you can see, its throughout the entire column on the same sheet.
Code isnt my strong point, however i'm very eager to learn!
Thanks again