This thread should probably be moved to "Off-Topic".
This is difficult to explain in words, but this is a "What-If Analysis" in Excel lingo. It allows you to examine the effects of changing an input (or two inputs) to a formula without having to re-key the formula with different cell references or copy the formula around the sheet.
Excel's reference page may be helpful, though you said you already did a search:
Calculating multiple results by using a data tableThe arrangement of cells is significant, but from the context of the calculation results, it looks like they are recalculating CellD for each of the WACC Assumption values (the top row of the "small table"). This might explain it better than I can, or things might "click" if you see this applied to a different situation.
The gist of it is you enter the formula to calculate the result for the base case (a formula with references to CellA and Cell B). Then, to the right of that, you enter the "What-If" cases for WACC Assumption. (Here, 16%, 18%, 20.7%, ...) Below the "base case" formula, you enter the "What-If" cases for Probability. You haven't shown this part, but since your TABLE function call uses two arguments, I assume it is there. See the reference link for cell arrangement for one-dimensional What-If analyses—things are slightly different then.
Once the formula and "What-If" cases are entered, select the full range of cells starting from the "base case" formula all the way out so that both dimensions of "What-If" inputs are selected. Then go to the Data tab on the ribbon and choose "What-If Analysis" from the "Data Tools" group. Choose "Data Table..." from the dropdown. Then you get a dialog from Excel asking for the Row and Column input cells. This tells Excel which cell reference should get replaced in the "base case" formula. So choose "CellA" for the "Row input cell" (What-If cases in the upper row of the table will replace CellA in the base formula) and "CellB" for the "Column input cell" (What-If cases in the left column of the table will replace CellB in the base formula). Clicking OK will fill in the table for each of the What-If scenarios.
The curly braces around the formula means that this is an array formula (it operates on ranges of cells, not individual cells) and in this case, you cannot enter this formula by hand. It has to be created using the "What-If Analysis" wizard.