How to use the Selection Tool
The Selection Tool 
is the primary tool in for moving and transforming objects on the canvas. It has its own array of options, shortcuts, and controls that will help speed up your design process.
When activated, the Selection Tools toolbar becomes available 
as well as the Transform controls 
, and the Object controls 
located in the control bar to the right (or bottom if using a phone).
Scaling the selection
By default the Selection Tool is in transform mode, but by simply tapping on the top right handle you can activate scale mode. Notice all other transform handles disappear. When activated, scale mode allows you to conveniently scale the selection evenly from its center point.
If you are using a mouse and keyboard you can scale the selection in transform mode by holding the shift key and pulling a handle to scale the selection in the direction of the handle. Holding shift + cmd (or ctrl key) will scale the selection from the center point.
Scaling may also be activated using the Constrain Tool 
in the Selection Tools toolbar together with the Scale From Center tool 
to scale the selection from its center point.
The Scale From Center tool without the Constrain Tool will stretch the selection from the center point.
Anchor the selection
Toggle on the Anchor Tool 
to activate the anchor handle on the canvas. Drag the anchor handle to the desired location to scale or rotate the selection around the anchor point.
Select Multiple
Multiple shapes may be selected at once by dragging the selection box completely over the objects you wish to add to the selection.
Shapes may be manually added to the selection by toggling on the Multiple Selection Tool 
then clicking the shapes you want to include into the selection, clicking the same shape again will remove the shape from the selection.
Duplicate the selection
Duplicate the selection using shift + cmd + D or by clicking the Duplicate Tool 
in the Selection Tools toolbar.
Delete the selection
Delete the selected objects by pressing the delete key or clicking the trash icon 
in the Selection Tools toolbar
Comments: 3
It should be possible to increase the setting of Grid Border to more than 1. I assume this is the size of the area for snapping to grid which is a very difficult operation. Also this area should become larger on the screen when zooming closer.
Is there a setting that makes it easier to switch from one object to another? (I keep moving the current object instead of selecting another, and working around it by switching away from the selection tool).
Not at the moment. You can switch from object to object simply by tapping on the object via the Selection Tool or by highlighting a group of objects. Do you use your desktop for editing? We’re working on keyboard shortcuts, and with that we can integrate a way to toggle through the objects using the keys.