How Do I Add Error Bars to My Plots?

Mathematica offers a number of powerful functions for presenting experimental error and drawing error bars. The two main ones are ErrorListPlot in the package Graphics`Graphics` and ErrorBar in the package MultipleListPlot. Both packages ship with Mathematica.

ErrorBar is the much more powerful function, and it is well documented in the package MultipleListPlot. So the discussion here is limited to the simpler ErrorListPlot.