The icon 
becomes visible when hovering the mouse over each element of the Graphic Modeling Area of the form, that allows to enter the side panel of properties that defines each of the different types of elements.
Types
Side Panel
In the side panel, the properties corresponding to each type of element can be displayed and modified. In the upper right part of it you can select icons to perform the following actions:
Actions
The icon 
is used to confirm the modifications made in the properties panel.
The icon 
is used to close the properties panel, if it was not previously saved, changes are discarded.
