Guides and grid can help you to arrange and align widgets on the page easily.
Grid
When the grid is activated a set of vertical and horizontal dotted lines are painted on the canvas background. If you also activate the "Snap to grid" option, when moving widgets through the canvas they will automatically align to the nearest grid line found.
To activate or deactivate the grid you can either go to the View menu and check/uncheck the option "Grid" or go to File->Preferences then select "User Interface" and check/uncheck the option "Show grid". In the Preferences dialog you can also find the following options to configure the grid:
Canvas size
Show grid
Snap to grid
Grid spacing
Snap to geometry
The option "Snap to geometry" can also assist you when positioning widgets on the page. When this option is on, vertical and horizontal guide lines appear while dragging a widget to indicate when it is aligned with other widgets on the page. The guide lines will appear following this criterion:
Dragging the widget horizontally, vertical lines appear on the left and right sides of other widgets meeting left and right side edges of the dragging widget.
Dragging the widget vertically, horizontal lines appear on the top and bottom sides of other widgets meeting top and bottom side edges of the dragging widget.
Horizontal and vertical lines will also appear together when the dragged widget's edges meet horizontal and vertical side edges of another widget on the page.
Hold Alt key while dragging the widget to avoid snapping.
To activate this option go to the View menu and check the option "Snap to geometry". You can find the same option in File->Preferences, inside the "User interface" section. The grid will never be shown when simulating a prototype.
Rulers
Rulers can be shown on the top and left sides of the canvas to assist you when positioning widgets.
To show or hide the rulers go to the View menu and check or uncheck the option "Rulers". This option can also be changed in the Preferences menu: go to File->Preferences, select "User interface" and check or uncheck the option "Show Rulers". In the preferences menu you can also change the units used by the rulers. Select there the option:Inches
Centimeters
Pixels (default option)
Ruler guides
Create horizontal or vertical guides on the rulers to help you align the widgets over an edge of great precision.
To create horizontal or vertical guides point the cursor over the position on the ruler you want to place the guide and left-click. Once a guide is created you can dragg it to change its position.
To remove a guide, right-click on its handler on the ruler and select the option "Remove guide". As an alternative you can press the 'Supr' key once selected.