To perform some functions such as interactively selecting elements of a layer using the selection tools, you must first make the elements of the layer selectable.
Pass the cursor over the card of the layer you are interested in to display the icon .
Click on to make the layer elements selectable. The icon is permanently displayed in the form.
Click on to make the elements of the layer non-selectable. The icon stops displaying and when you pass the cursor over the card, the icon appears.