"…the formula in C2 and it worked for that row, but how do I get it to go down the entire column?"
Click on the last cell containing the formula, then place the pointer near the bottom border of that cell.
The yellow dot that appears in the Fill control. Place the pointer on the dot—the pointer will change to a pair of arrows pointing up and down, with a horizontal line separating then. Click and hold the mouse button and drag down to fill the formula into the rows below.

The image shows the starting position, but was taken after I had filled the cells in rows 11 to 15.
Once you have the formula filled to the bottom cell in the column, Numbers will automatically fill it into new rows added to the column (which is what actually happened in this table whenI added those five rows by dragging the Row control, seen below the row reference tab for row 15, down to add five rows.
If you have a very long column, you may find this alternate method more efficient:
Select the last cell containing the formula. Press command-C to copy the cell and its contents.
Scroll to the last cell in the column.
Chift-click (press and hold the shift key then click) on that cell.
Press command-V to Paste the formula into all selected cells.
In either case, Numbers will automatically adjust the cell reference to fit the row containing each copy of the formula.
The TODAY function returns today's date. TODAY recalculates whenever there is a change in the table containing the function.
The change can be as small as clicking a checkbox cell to change its value from FALSE to TRUE (or vice versa).
Regards,
Barry