Creating a macro to SUM a varying range of cells

First: Hello all, greetings!

Second: I am completely worthless when it comes to programming, so it was much simpler to just ask this here. I tried several variations on some automatically generated macros, but none of them worked.

Now: I need a macro to create a SUM formula based on selected cells, and it needs to appear in a single cell relative to the cells I selected. Here's some screens demonstrating what I need:
1: Select some cells
\1

2: SUM them up in that cell there
\1

3: Done
\1

Thank you!

It would help to know how you are using the spreadsheet. ie what is the spreadsheet doing.

Perhaps something like

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Ah sorry. I forgot that that would be the most logical. Here's a sample sheet wtihout all my sensitive information on it:

EDIT: Mike, I tried your thing, and it worked perfectly. A little editing of it, and I figured out exactly what I needed! Thanks again!