I also use google calendar. Even as very non technical I find it easy to use.
Being rather old fashioned I also keep a paper calendar which I update in pen and amend with white out. There have been a couple of occasions where I have had technology issues, or have been in an ashram where online time is limited, or had other issues where having the paper has been helpful. I also find if I color code regular sessions one color, and subbing in another I am more likely to give extra notice so I do not forget a change in my schedule that day.