If you are importing the data to the experiment setup window and then displaying the data cache in the graph window, error bars may be added to the imported data. Click on the graph setup icon (in the lower lefthand corner of the graph window) and set the parameters for the horizontal and/or vertical error bars (chose a fixed error value or as a percent of the coordinate). Click OK.
If you are using the match data option in the graph window to load your data cache, the plot will show black connected lines, not individual data points. There is not a way to add error bars to the line.