Really basic question...

Really basic question is countdown -= Time.deltaTime; the same as countdown = countdown - Time.deltaTime; Im new to coding so i don’t know. Please help.

Yes it is. You can do the same with +=, *=, /= and so on.

Another handy shortcut operator for incrementing and decrementing is the ++ or – operator…

x++;
y–;

is the same as
x = x + 1, or x += 1
y = y - 1 or y–