Here are some common methods of the DateTime class with a brief description of what they do:

1. now(): Returns a DateTime object representing the current date and time.

2. date(): Returns a new DateTime object with the same year, month, and day, but with the time set to midnight.

3. time(): Returns a new DateTime object with the same time, but with the date set to January 1, 1 (the minimum valid date in the .NET Framework).

4. year(): Returns the year of the DateTime object.

5. month(): Returns the month of the DateTime object.

6. day(): Returns the day of the month of the DateTime object.

7. hour(): Returns the hour of the DateTime object.

8. minute(): Returns the minute of the DateTime object.

9. second(): Returns the second of the DateTime object.

10. dayofweek(): Returns the day of the week of the DateTime object.

11. adddays(days): Returns a new DateTime object with the specified number of days added.

12. addhours(hours): Returns a new DateTime object with the specified number of hours added.

13. addminutes(minutes): Returns a new DateTime object with the specified number of minutes added.

14. addseconds(seconds): Returns a new DateTime object with the specified number of seconds added.

15. addmonths(months): Returns a new DateTime object with the specified number of months added.

16. addyears(years): Returns a new DateTime object with the specified number of years added.

17. subtract(other): Returns a TimeSpan object representing the difference between the current DateTime object and the specified DateTime object.

18. tostring(format): Returns a string representation of the DateTime object using the specified format.

19. parse(str, format): Converts the specified string representation of a date and time to its DateTime equivalent using the specified format.

20. tryparse(str, dt): Converts the specified string representation of a date and time to its DateTime equivalent using the specified format, and returns a value indicating whether the conversion succeeded.