There are two functions, NOW and TODAY that lets you insert time and date in google sheets instead of manually typing times and dates. Since these functions are dynamic, it updates the date and time based on real time as the spreadsheet changes or on a regular basis.
Using NOW function
The NOW function needs no extra arguments and can not only show date but also current time with proper formatting. Just select an empty cell and type =NOW() to use it. You can choose between showing both date and time, only date or only time. Just select the cell with the NOW function used and click Format>Number and choose the appropriate option among Date, Time and Date and Time.
You can also set the format of the time shown. Normally google will use the format best suited based on your locality by default but you may change it to the format you want. Click File>Settings and choose your preferred locale to change to that format(Note that changing this will also change the format of any currency related data in your spreadsheet). You can also set the time zone to use a separate time than your local time.
The time generated by this function will usually update every time any changes are made to the spreadsheet. You can change it to update every minute or every hour according to your preferences. Click File>Settings and open the calculation tab and choose the desired option under “Recalculation”.
Using the TODAY function
Just like the NOW function, TODAY function also does not need any extra arguments but displays the current date only not time. Select an empty cell and type =TODAY() to use it. The format is set to your local format by default.
Inserting Non-dynamic Date/Time
If you wish to enter the current date/time but do not want it to update automatically, you cannot use these functions for that. Although instead of manually typing there are two keyboard shortcuts.
Press Ctrl+;(semicolon) on the keyboard to enter the current date.
Press Ctrl+Shift+:(colon) on the keyboard to enter the current time.