How can brushing be used in exploratory data analysis?
There are countless applications of brushing to explore relationships between variables and/or the contribution of specific data points or subsets to those relationships.

A "typical" illustration of the use of brushing in exploratory data analysis is the examination of the contribution of data points representing different ranges or different levels of one variable to correlations between other variables, which can be inspected visually using a scatterplot matrix. For example, by including a categorical, three-level variable such as income level (Income) in a scatterplot matrix (see above), then by using the Box, Lasso, or Slice X brush, points can be selected from one income level, and the location of these points in scatterplots of all other variables (e.g., Assets, Debt) becomes immediately apparent.​

1.When the graph is active, click "Brushing" icon(circled in red) under Edit tab to prompt "Brushing 2D" dialog

2. In the "Brushing 2D" dialog|Interactive tab, choose actions(Mark/label/Off) you want to perform under Actions (help document for "Actions"). 

Note: the color and pattern for the marker can be customized under Action|Color/Marker drill down list. 

3. Under Selection Brush, select the the type of brush to highlight the data points that you want to mark/label on the graph.

4. Check the "Auto Apply" if you want the brushing action automatically applied to the graph. Otherwise, click "Apply" after you perform brushing on the graph

5. hover over the graph and highlight data points you want to brush, the brushing actions will be performed on those points. For instance, the data point with case ID # 118 is labelled on all my graph