How to insert the current date or time
The first way is to write date right into the cell or to use the shortcuts:
Ctrl+; enters the current date.
Ctrl+: enters the current time.
This method ensures that the cell will always has the date which you have written into it.
If you need date changing always to current, you have to use Date & Time functions.
To insert the current date use the function TODAY(). To insert the current date and time use the function NOW(). These functions do not require any arguments.