Connection Line tool will allow you to link objects on the board. This is helpful for building diagrams and flowcharts.
To create a line, select Connection Line on the toolbar or press L on your keyboard, click an object and drag your cursor to another object. You can also select an object and click one of the blue dots around it to start drawing a link.
Specify arrowheads, line and stroke type, thickness, color etc. in the Connection Line menu:
To draw a straight horizontal, vertical, or diagonal line, hold Shift. To disable snapping to other objects hold Ctrl (Cmd).
Drawing a straight line and a standalone line
Adding text labels
Each diagram item is meaningful, and lines are not an exception. To establish clearer relations between objects on your boards use text labels.
Double-click any connection line or click +T in the context menu to start entering the text. Fix it horizontally or let the text follow line curves.
Adding a text lable to the line