=NOW()
However, to get the current date only use the TODAY() function.
To get the current time only use =NOW()-TODAY(). However, you have to change cell format to Time from category.
However, you can also use these keybord shortcuts to enter current date and time into your cell:
Enter the current date Ctrl+Shift+semi-colon (; )
Enter the current time Ctrl+Shift+colon (: )
Further use (just copy and paste into your excell file to test),
You can also use the NOW() function to get your any targeted date and time.
=NOW()-0.5
Returns the date and time 12 hours ago (-0.5 days ago)
=NOW()-0.25
Returns the date and time 6 hours ago (-0.25 days ago)
=NOW()-2.0
Returns the date and time 2 days ago (-2.0 days ago)
=NOW()-2.25
Returns the date and time 2 days and 6 hours ago (-2.25 days ago)
=NOW()-2.5
Returns the date and time 2 days and 12 hours ago (-2.5 days ago)
=NOW()+5
Returns the date and time 5 days in the future(+5 days)
You may also consult Microsoft page here