You can group your process activities on the canvas by adding swimlanes or colourful text boxes.  Both allow you to highlight specific groupings, process areas or parallel flows within the same process.

You can add swimlanes in any diagram. Switch to edit mode, and select the "Swimlanes" tab in the right panel. Click on "Add new" to add a new swimlane.

The first new swimlane will appear on the canvas horizontally, with its starting point in the upper-left section of the currently displayed part of the canvas. You can control the length of all swimlanes using the +/- buttons and also the width, colors, and fonts of individual swimlanes.

You can remove any individual swimlane at any point using the "X" icon in the right panel, or drag and drop it within the "Swimlanes" tab to re-order the swimlanes. 

There is no limit to the number of swimlanes you can have on a diagram, and they can be either horizontal or vertical (use the "Switch flow" button to flip between horizontal/vertical). The swimlanes are a diagram's “background”, so they do not control the positioning of activity boxes and can be switched on or off at will. The placing of an activity box on a swimlane provides a visual cue, but does not have any meaning or relationship at a system level within Elements. The resource defines the responsibility for an activity. 

See also this short video snippet:

If swimlanes are too heavy and inflexible for what you are trying to accomplish, then you could use text boxes to highlight some process areas, like this:

When in edit mode, open up the left tools panel and drag and drop a text box into the canvas. Double-click on the text box to change the text. Click on it once to open up its right panel where you can customize its colors, fonts, and attachments.