Attachment is the association and linking of one tool with another and the attachment defines how they interact and move with respect to each other.
The workspace tools located along the bottom of the screen are used to analyze the current geometric shape (e.g., triangle). Tools such as, points, lines, and circles can be dragged and dropped on key locations in the workspace, directly on the primary geometric shape, or on other tools. Dropping the point, line, or circle on the shape effectively attaches itself to the shape. For example points can be dragged and dropped on a line, perimeter of a circle, intersection of lines and circles, and many other locations. Dropping a tool onto another tool or shape creates a child-parent attachment relationship. Another example is that lines can be attached perpendicularly or parallel to other lines as well as a tangent line on the perimeter of a circle. When you drag the parent shape or tool, the child tool moves as well. You simply detach them by moving the child from the parent.
Image below shows attaching a circle perimeter to a shape point. Several options are given and by quickly rolling your finger to the left or right you change the selected drop point (association).