Auto populate ID field of a new row
By magic? No such thing in Excel or any other spreadsheet.
=IF(AND(A1<>"";B2<>"");A1+1;"") <- Enter in A2 and "fill down"
e.g. Copy A2 (i.e. Place cursor in A2, CTRL+C), then...
Paste, CTRL+V, into as many rows as you wish, in column A.
Fill in a value in A1, type something in B1 - first row.
Then type something in B2, B3, B4 ...
The extreme would be ALL rows, which might slow down your spreadsheet
it is really quickly done though:
Excel:
hit End, hold SHIFT, hit Cursor down, let go of SHIFT,
CTRL+V, End, Cursor up
LibreOffice:
hold SHIFT and CTRL, hit Cursor down, let go
CTRL+V, hold CTRL, hit Cursor up
... and you have the formula in all cells of the A column, except A1.