Select the topic whose subtopics you want to group with the boundary.
Click the Boundary
button 
on the main toolbar and choose the boundary type.
Boundaries come in two basic types: grouping boundaries and summary boundaries.
Grouping boundaries can be used to emphasize the relationships between topics and subtopics with an outline surrounding an area on a map with your choice of line type and an optional fill color.
Summary boundaries can be used to reduce a set of subtopics into a single summary topic and then allow this topic to grow again.
You can add boundaries within boundaries. The default boundary formatting is determined by the style settings. Boundaries are not shown in Outline view.
To create a boundary:
Select the topic whose subtopics you want to group with the boundary.
Click the Boundary
button on the main toolbar and choose the boundary type.
Select the boundary (a blue box shows it is selected).
Right-click and select Format Boundary or click Format - Boundary.
Hint:
You can use the buttons on the bottom formatting toolbar to set the boundary
Line color or 
Fill
color. If you choose one of the Summary boundary types the fill color
will be disabled.
To add a summary topic to a summary boundary:
Select the boundary (a blue box shows it is selected).
Click the Insert
Callout 
button or click Insert
- Callout Topic.
Hint: You can expand the summary topic into a new topic tree by adding subtopics to it.
To remove a boundary:
Select the boundary (a blue box shows it is selected)
and press Del
or
Right-click the boundary and select
Delete Boundary.
Shortcut: to
create a boundary of the same style as an existing boundary you can copy
the boundary to a new topic tree.
Right-click on the boundary and use the Cut,
Copy, and Paste
commands.
