How do I add standard error or standard deviation error bars to a bar graph in common software like Excel or Python?

In Excel, you can add error bars via the 'Add Chart Element' -> 'Error Bars' menu. You can specify a fixed value, percentage, standard deviation, standard error, or custom values. In Python using libraries like Matplotlib or Seaborn, functions like `plt.errorbar` or `sns.barplot` with the `yerr` parameter allow you to specify the error bar values calculated beforehand.