To draw a line, just click and drag from the edge of a shape. When you release your mouse, the shape auto-prompt will appear. To turn off auto-prompt, click 'File' in the Menu bar, select 'Preferences', then choose the desired option.
As you drag an object on the canvas, lines will appear to help you easily align the new shape with existing shapes on the canvas. Note: If you have "Snap To Grid" enabled, objects will still snap to grid, which may conflict with this auto alignment method. If you would like to use this alignment method, we recommend disabling snap to grid (see below for more information).
You can also align multiple objects relative to each other. Just follow these steps:
Select all of the objects by holding down ctrl (cmd for mac) and clicking on each object individually, or by dragging and selecting all of them at once.
Right-click and go to the "Align" menu
Choose the alignment relationship. You'll see a preview of the new alignment in the background.
The third alignment method is "Snap to Grid." By default, documents are set to snap to "Normal grid (20px)." You can change this setting from the "Page Settings" panel of the dock on the right-hand side of the editor.